diff --git a/src/main/java/se/issuetrackingsystem/comment/controller/CommentController.java b/src/main/java/se/issuetrackingsystem/comment/controller/CommentController.java
index c29cd2a..1ffc36b 100644
--- a/src/main/java/se/issuetrackingsystem/comment/controller/CommentController.java
+++ b/src/main/java/se/issuetrackingsystem/comment/controller/CommentController.java
@@ -1,5 +1,6 @@
 package se.issuetrackingsystem.comment.controller;
 
+import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.http.ResponseEntity;
@@ -21,7 +22,7 @@ public class CommentController {
     private final CommentService commentService;
 
     @PostMapping
-    public ResponseEntity<List<CommentResponse>> commentCreate(@RequestParam("issueId") Long issueId,@RequestBody CommentRequest commentRequest){
+    public ResponseEntity<List<CommentResponse>> commentCreate(@RequestParam("issueId") Long issueId, @Valid @RequestBody CommentRequest commentRequest){
         commentService.create(issueId,commentRequest.getMessage(),commentRequest.getAuthorId());
         List<Comment> comments = commentService.getList(issueId);
         List<CommentResponse> responses = new ArrayList<>();
@@ -37,7 +38,7 @@ public ResponseEntity<Comment> commentDelete(@RequestParam("commentId") Long com
     }
 
     @PatchMapping
-    public ResponseEntity<Comment> commentModify(@RequestParam("commentId") Long commentId, @RequestBody CommentRequest commentRequest){
+    public ResponseEntity<Comment> commentModify(@RequestParam("commentId") Long commentId, @Valid @RequestBody CommentRequest commentRequest){
         return ResponseEntity.ok(commentService.modify(commentId, commentRequest.getMessage()));
     }
 
diff --git a/src/main/java/se/issuetrackingsystem/comment/dto/CommentRequest.java b/src/main/java/se/issuetrackingsystem/comment/dto/CommentRequest.java
index 1bcac7c..ddba1bc 100644
--- a/src/main/java/se/issuetrackingsystem/comment/dto/CommentRequest.java
+++ b/src/main/java/se/issuetrackingsystem/comment/dto/CommentRequest.java
@@ -8,9 +8,9 @@
 @Getter
 @Setter
 public class CommentRequest {
-    @NotBlank
+
+    @NotBlank(message = "Message는 공백이 될 수 없습니다.")
     private String message;
 
-    @NotBlank
     private Long authorId;
-}
+}
\ No newline at end of file
diff --git a/src/main/java/se/issuetrackingsystem/common/exception/ErrorCode.java b/src/main/java/se/issuetrackingsystem/common/exception/ErrorCode.java
index 4d15962..c7e5a87 100644
--- a/src/main/java/se/issuetrackingsystem/common/exception/ErrorCode.java
+++ b/src/main/java/se/issuetrackingsystem/common/exception/ErrorCode.java
@@ -12,13 +12,13 @@ public enum ErrorCode {
      * 400 BAD_REQUEST: 잘못된 요청
      */
     BAD_REQUEST(HttpStatus.BAD_REQUEST, "잘못된 요청입니다."),
+    ROLE_BAD_REQUEST(HttpStatus.BAD_REQUEST, "역할이 올바르지 않습니다."),
+    PASSWORD_BAD_REQUEST(HttpStatus.BAD_REQUEST, "비밀번호가 올바르지 않습니다."),
 
     /*
      * 403 Forbidden: 승인을 거부함
      */
     USERNAME_FORBIDDEN(HttpStatus.FORBIDDEN, "존재하는 회원 이름입니다."),
-    ROLE_FORBIDDEN(HttpStatus.FORBIDDEN, "역할이 올바르지 않습니다."),
-    PASSWORD_FORBIDDEN(HttpStatus.FORBIDDEN, "비밀번호가 올바르지 않습니다."),
 
     /*
      * 404 NOT_FOUND: 리소스를 찾을 수 없음
diff --git a/src/main/java/se/issuetrackingsystem/common/exception/GlobalExceptionHandler.java b/src/main/java/se/issuetrackingsystem/common/exception/GlobalExceptionHandler.java
index 5e79125..e4ebef3 100644
--- a/src/main/java/se/issuetrackingsystem/common/exception/GlobalExceptionHandler.java
+++ b/src/main/java/se/issuetrackingsystem/common/exception/GlobalExceptionHandler.java
@@ -1,11 +1,17 @@
 package se.issuetrackingsystem.common.exception;
 
 import lombok.extern.slf4j.Slf4j;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
+import org.springframework.validation.FieldError;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
+import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.RestControllerAdvice;
 
+import java.util.HashMap;
+import java.util.Map;
+
 @RestControllerAdvice
 @Slf4j
 public class GlobalExceptionHandler {
@@ -21,6 +27,20 @@ protected ResponseEntity<ErrorResponse> handleCustomException(final CustomExcept
                 .body(new ErrorResponse(e.getErrorCode()));
     }
 
+    /*
+     * 유효성 검사 오류 메시지 반환
+     * */
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    protected ResponseEntity<Map<String, String>> handleValidationExceptions(MethodArgumentNotValidException e) {
+        Map<String, String> errors = new HashMap<>();
+        e.getBindingResult().getAllErrors().forEach((error) -> {
+            String fieldName = ((FieldError) error).getField();
+            String errorMessage = error.getDefaultMessage();
+            errors.put(fieldName, errorMessage);
+        });
+        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(errors);
+    }
+
     /*
      * HTTP 405 Exception
      * */
diff --git a/src/main/java/se/issuetrackingsystem/issue/controller/IssueController.java b/src/main/java/se/issuetrackingsystem/issue/controller/IssueController.java
index a841672..5747d5d 100644
--- a/src/main/java/se/issuetrackingsystem/issue/controller/IssueController.java
+++ b/src/main/java/se/issuetrackingsystem/issue/controller/IssueController.java
@@ -1,6 +1,7 @@
 package se.issuetrackingsystem.issue.controller;
 
 
+import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.http.ResponseEntity;
@@ -24,7 +25,7 @@ public class IssueController {
     private final IssueService issueService;
 
     @PostMapping
-    public ResponseEntity<List<IssueResponse>> issueCreate(@RequestBody IssueRequest issueRequest, @RequestParam("projectId") Long projectId){
+    public ResponseEntity<List<IssueResponse>> issueCreate(@Valid @RequestBody IssueRequest issueRequest, @RequestParam("projectId") Long projectId){
         issueService.create(projectId,issueRequest.getTitle(),issueRequest.getDescription(),issueRequest.getUserid(),issueRequest.getPriority());
         List<Issue> issues = issueService.getList(projectId);
         List<IssueResponse> responses = new ArrayList<>();
@@ -57,13 +58,13 @@ public ResponseEntity<IssueResponse> issueDelete(@RequestParam("issueId") Long i
     }
 
     @PatchMapping
-    public ResponseEntity<IssueResponse> issueModify(@RequestBody IssueRequest issueRequest,@RequestParam("issueId") Long issueId){
+    public ResponseEntity<Issue> issueModify(@Valid @RequestBody IssueRequest issueRequest,@RequestParam("issueId") Long issueId){
         Issue issue = issueService.modify(issueId,issueRequest.getTitle(),issueRequest.getDescription(),issueRequest.getPriority(),issueRequest.getUserid());
         return ResponseEntity.ok(new IssueResponse(issue));
     }
 
     @PostMapping("/assignees")
-    public ResponseEntity<IssueResponse> issueSetAssignee(@RequestBody IssueRequest issueRequest,@RequestParam("issueId") Long issueId){
+    public ResponseEntity<Issue> issueSetAssignee(@Valid @RequestBody IssueRequest issueRequest,@RequestParam("issueId") Long issueId){
         Issue issue = issueService.setAssignee(issueId,issueRequest.getUserid(),issueRequest.getAssigneeId());
         return ResponseEntity.ok(new IssueResponse(issue));
     }
@@ -79,7 +80,7 @@ public ResponseEntity<List<IssueResponse>> issueCheckByStatus(@PathVariable("sta
     }
 
     @PatchMapping("/status")
-    public ResponseEntity<IssueResponse> issueChangeStatus(@RequestBody IssueRequest issueRequest,@RequestParam("issueId") Long issueId){
+    public ResponseEntity<Issue> issueChangeStatus(@Valid @RequestBody IssueRequest issueRequest,@RequestParam("issueId") Long issueId){
         Issue issue = issueService.changeStatus(issueRequest.getUserid(),issueId);
         return ResponseEntity.ok(new IssueResponse(issue));
     }
diff --git a/src/main/java/se/issuetrackingsystem/issue/dto/IssueRequest.java b/src/main/java/se/issuetrackingsystem/issue/dto/IssueRequest.java
index 3f2ad22..170b31b 100644
--- a/src/main/java/se/issuetrackingsystem/issue/dto/IssueRequest.java
+++ b/src/main/java/se/issuetrackingsystem/issue/dto/IssueRequest.java
@@ -1,5 +1,6 @@
 package se.issuetrackingsystem.issue.dto;
 
+import jakarta.validation.constraints.NotBlank;
 import lombok.Getter;
 import lombok.Setter;
 import se.issuetrackingsystem.issue.domain.Issue;
@@ -7,6 +8,8 @@
 @Getter
 @Setter
 public class IssueRequest {
+
+    @NotBlank(message = "Title은 공백이 될 수 없습니다.")
     private String title;
 
     private String description;
@@ -15,7 +18,7 @@ public class IssueRequest {
 
     private Issue.Status status;
 
-    private Long userid;
+    private Long userId;
 
     private Long assigneeId;
 
diff --git a/src/main/java/se/issuetrackingsystem/issue/service/IssueService.java b/src/main/java/se/issuetrackingsystem/issue/service/IssueService.java
index d38e1f2..c794f43 100644
--- a/src/main/java/se/issuetrackingsystem/issue/service/IssueService.java
+++ b/src/main/java/se/issuetrackingsystem/issue/service/IssueService.java
@@ -99,7 +99,7 @@ public Issue setAssignee(Long issueId, Long userId, Long assigneeId){
         User user = userRepository.findById(userId).orElseThrow(() -> new CustomException(ErrorCode.USER_NOT_FOUND));
         User assignee = userRepository.findById(assigneeId).orElseThrow(() -> new CustomException(ErrorCode.USER_NOT_FOUND));
         if (!user.canSetAssignee()||!assignee.canChangeIssueStateAssignedToFixed()) {
-            throw new CustomException(ErrorCode.ROLE_FORBIDDEN);
+            throw new CustomException(ErrorCode.ROLE_BAD_REQUEST);
         }
         issue.setAssignee(assignee);
         issue.setStatus(Issue.Status.ASSIGNED);
diff --git a/src/main/java/se/issuetrackingsystem/project/controller/ProjectController.java b/src/main/java/se/issuetrackingsystem/project/controller/ProjectController.java
index 4b4b3a9..eb643b6 100644
--- a/src/main/java/se/issuetrackingsystem/project/controller/ProjectController.java
+++ b/src/main/java/se/issuetrackingsystem/project/controller/ProjectController.java
@@ -1,5 +1,6 @@
 package se.issuetrackingsystem.project.controller;
 
+import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
@@ -17,7 +18,7 @@ public class ProjectController {
     private final ProjectService projectService;
 
     @PostMapping
-    public ResponseEntity<ProjectResponse> createProject(@RequestBody ProjectRequest request) {
+    public ResponseEntity<ProjectResponse> createProject(@Valid @RequestBody ProjectRequest request) {
         return ResponseEntity.ok(projectService.createProject(request));
     }
 
diff --git a/src/main/java/se/issuetrackingsystem/project/dto/ProjectRequest.java b/src/main/java/se/issuetrackingsystem/project/dto/ProjectRequest.java
index ce886f8..245cd60 100644
--- a/src/main/java/se/issuetrackingsystem/project/dto/ProjectRequest.java
+++ b/src/main/java/se/issuetrackingsystem/project/dto/ProjectRequest.java
@@ -10,12 +10,10 @@
 @RequiredArgsConstructor
 public class ProjectRequest {
 
-    @NotBlank
+    @NotBlank(message = "Title은 공백이 될 수 없습니다.")
     private final String title;
 
-    @NotBlank
     private final Long adminId;
 
     private final List<Long> contributorIds;
-
 }
diff --git a/src/main/java/se/issuetrackingsystem/user/controller/UserController.java b/src/main/java/se/issuetrackingsystem/user/controller/UserController.java
index 314861e..7ab24d1 100644
--- a/src/main/java/se/issuetrackingsystem/user/controller/UserController.java
+++ b/src/main/java/se/issuetrackingsystem/user/controller/UserController.java
@@ -1,5 +1,6 @@
 package se.issuetrackingsystem.user.controller;
 
+import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
@@ -18,12 +19,12 @@ public class UserController {
     private final UserService userService;
 
     @PostMapping("/register")
-    public ResponseEntity<UserResponse> register(@RequestBody RegisterRequest request) {
+    public ResponseEntity<UserResponse> register(@Valid @RequestBody RegisterRequest request) {
         return ResponseEntity.ok(userService.register(request));
     }
 
     @PostMapping("/login")
-    public ResponseEntity<UserResponse> login(@RequestBody LoginRequest request) {
+    public ResponseEntity<UserResponse> login(@Valid @RequestBody LoginRequest request) {
         return ResponseEntity.ok(userService.login(request));
     }
 
diff --git a/src/main/java/se/issuetrackingsystem/user/dto/LoginRequest.java b/src/main/java/se/issuetrackingsystem/user/dto/LoginRequest.java
index 752b258..d06762f 100644
--- a/src/main/java/se/issuetrackingsystem/user/dto/LoginRequest.java
+++ b/src/main/java/se/issuetrackingsystem/user/dto/LoginRequest.java
@@ -8,9 +8,9 @@
 @RequiredArgsConstructor
 public class LoginRequest {
 
-    @NotBlank
+    @NotBlank(message = "Username은 공백이 될 수 없습니다.")
     private final String username;
 
-    @NotBlank
+    @NotBlank(message = "Password는 공백이 될 수 없습니다.")
     private final String password;
 }
diff --git a/src/main/java/se/issuetrackingsystem/user/dto/RegisterRequest.java b/src/main/java/se/issuetrackingsystem/user/dto/RegisterRequest.java
index 9b62cec..b78f5af 100644
--- a/src/main/java/se/issuetrackingsystem/user/dto/RegisterRequest.java
+++ b/src/main/java/se/issuetrackingsystem/user/dto/RegisterRequest.java
@@ -8,12 +8,12 @@
 @RequiredArgsConstructor
 public class RegisterRequest {
 
-    @NotBlank
+    @NotBlank(message = "Username은 공백이 될 수 없습니다.")
     private final String username;
 
-    @NotBlank
+    @NotBlank(message = "Password는 공백이 될 수 없습니다.")
     private final String password;
 
-    @NotBlank
+    @NotBlank(message = "Role은 공백이 될 수 없습니다.")
     private final String role;
 }
\ No newline at end of file
diff --git a/src/main/java/se/issuetrackingsystem/user/dto/UserResponse.java b/src/main/java/se/issuetrackingsystem/user/dto/UserResponse.java
index 6242f4e..fddfa09 100644
--- a/src/main/java/se/issuetrackingsystem/user/dto/UserResponse.java
+++ b/src/main/java/se/issuetrackingsystem/user/dto/UserResponse.java
@@ -7,13 +7,8 @@
 @Getter
 public class UserResponse {
 
-    @NotBlank
     private final Long userId;
-
-    @NotBlank
     private final String username;
-
-    @NotBlank
     private final String role;
 
     public UserResponse(User user) {
diff --git a/src/main/java/se/issuetrackingsystem/user/repository/UserRepository.java b/src/main/java/se/issuetrackingsystem/user/repository/UserRepository.java
index 758630d..22ba2e6 100644
--- a/src/main/java/se/issuetrackingsystem/user/repository/UserRepository.java
+++ b/src/main/java/se/issuetrackingsystem/user/repository/UserRepository.java
@@ -1,6 +1,7 @@
 package se.issuetrackingsystem.user.repository;
 
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
 import org.springframework.stereotype.Repository;
 import se.issuetrackingsystem.user.domain.User;
 
@@ -10,4 +11,7 @@
 @Repository
 public interface UserRepository extends JpaRepository<User, Long> {
     Optional<User> findByUsername(String username);
+
+    @Query("SELECT u FROM users u WHERE TYPE(u) IN (PL, Dev, Tester)")
+    Optional<List<User>> findContributors();
 }
diff --git a/src/main/java/se/issuetrackingsystem/user/service/UserService.java b/src/main/java/se/issuetrackingsystem/user/service/UserService.java
index 0be7f47..f7444ce 100644
--- a/src/main/java/se/issuetrackingsystem/user/service/UserService.java
+++ b/src/main/java/se/issuetrackingsystem/user/service/UserService.java
@@ -50,7 +50,7 @@ public UserResponse login(LoginRequest request) {
                 .orElseThrow(() -> new CustomException(ErrorCode.USER_NOT_FOUND));
 
         if (!passwordEncoder.matches(request.getPassword(), user.getPassword())) {
-            throw new CustomException(ErrorCode.PASSWORD_FORBIDDEN);
+            throw new CustomException(ErrorCode.PASSWORD_BAD_REQUEST);
         }
 
         return new UserResponse(user);
@@ -66,6 +66,18 @@ public List<UserResponse> getUsers() {
                 .toList();
     }
 
+    @Transactional(readOnly = true)
+    public List<UserResponse> getContributors() {
+
+        List<User> users = userRepository.findContributors()
+                .orElseThrow(() -> new CustomException(ErrorCode.USER_NOT_FOUND));
+
+        return users
+                .stream()
+                .map(UserResponse::new)
+                .toList();
+    }
+
     private boolean isDuplicateUsername(String username) {
         Optional<User> user = userRepository.findByUsername(username);
         return user.isPresent();
@@ -77,7 +89,7 @@ private User createUser(String role, String username, String password) {
             case "PL" -> new PL(username, password);
             case "Dev" -> new Dev(username, password);
             case "Tester" -> new Tester(username, password);
-            default -> throw new CustomException(ErrorCode.ROLE_FORBIDDEN);
+            default -> throw new CustomException(ErrorCode.ROLE_BAD_REQUEST);
         };
     }
 }
diff --git a/src/test/java/se/issuetrackingsystem/user/service/UserServiceTest.java b/src/test/java/se/issuetrackingsystem/user/service/UserServiceTest.java
index 6c01f5a..4d925d2 100644
--- a/src/test/java/se/issuetrackingsystem/user/service/UserServiceTest.java
+++ b/src/test/java/se/issuetrackingsystem/user/service/UserServiceTest.java
@@ -10,6 +10,7 @@
 import org.springframework.transaction.annotation.Transactional;
 import se.issuetrackingsystem.common.exception.CustomException;
 import se.issuetrackingsystem.common.exception.ErrorCode;
+import se.issuetrackingsystem.user.domain.Admin;
 import se.issuetrackingsystem.user.domain.Dev;
 import se.issuetrackingsystem.user.domain.Tester;
 import se.issuetrackingsystem.user.dto.LoginRequest;
@@ -99,4 +100,17 @@ void getUsers() {
         assertTrue(response.stream().anyMatch(u -> "TestDev".equals(u.getUsername())));
         assertTrue(response.stream().anyMatch(u -> "TestTester".equals(u.getUsername())));
     }
+
+    @Test
+    void getContributors() {
+        Admin user1 = new Admin("TestAdmin", passwordEncoder.encode("0000"));
+        Tester user2 = new Tester("TestTester", passwordEncoder.encode("0000"));
+        userRepository.save(user1);
+        userRepository.save(user2);
+
+        List<UserResponse> response = userService.getContributors();
+
+        assertEquals(1, response.size());
+        assertTrue(response.stream().anyMatch(u -> "TestTester".equals(u.getUsername())));
+    }
 }
\ No newline at end of file