diff --git a/crates/voicevox_core/src/__internal/interop.rs b/crates/voicevox_core/src/__internal/interop.rs
index fce2ad0ed..0085a3222 100644
--- a/crates/voicevox_core/src/__internal/interop.rs
+++ b/crates/voicevox_core/src/__internal/interop.rs
@@ -1,6 +1,7 @@
 pub mod raii;
 
 pub use crate::{
+    convert::ToJsonValue,
     metas::merge as merge_metas,
     synthesizer::{
         blocking::PerformInference, DEFAULT_CPU_NUM_THREADS, DEFAULT_ENABLE_INTERROGATIVE_UPSPEAK,
diff --git a/crates/voicevox_core/src/convert.rs b/crates/voicevox_core/src/convert.rs
new file mode 100644
index 000000000..d7851c724
--- /dev/null
+++ b/crates/voicevox_core/src/convert.rs
@@ -0,0 +1,7 @@
+pub trait ToJsonValue {
+    fn to_json_value(&self) -> serde_json::Value;
+
+    fn to_json(&self) -> String {
+        self.to_json_value().to_string()
+    }
+}
diff --git a/crates/voicevox_core/src/devices.rs b/crates/voicevox_core/src/devices.rs
index cdf59f872..4b49456be 100644
--- a/crates/voicevox_core/src/devices.rs
+++ b/crates/voicevox_core/src/devices.rs
@@ -7,6 +7,8 @@ use std::{
 use derive_more::BitAnd;
 use serde::Serialize;
 
+use crate::convert::ToJsonValue;
+
 pub(crate) fn test_gpus(
     gpus: impl IntoIterator<Item = GpuSpec>,
     inference_rt_name: &'static str,
@@ -124,8 +126,10 @@ impl SupportedDevices {
     } else {
         panic!("either `load-onnxruntime` or `link-onnxruntime` must be enabled");
     };
+}
 
-    pub fn to_json(self) -> serde_json::Value {
+impl ToJsonValue for SupportedDevices {
+    fn to_json_value(&self) -> serde_json::Value {
         serde_json::to_value(self).expect("should not fail")
     }
 }
diff --git a/crates/voicevox_core/src/lib.rs b/crates/voicevox_core/src/lib.rs
index 2495d685a..14beee6f1 100644
--- a/crates/voicevox_core/src/lib.rs
+++ b/crates/voicevox_core/src/lib.rs
@@ -49,6 +49,7 @@ const _: () = {
 };
 
 mod asyncs;
+mod convert;
 mod core;
 mod devices;
 /// cbindgen:ignore
diff --git a/crates/voicevox_core_c_api/src/compatible_engine.rs b/crates/voicevox_core_c_api/src/compatible_engine.rs
index 793a224c8..eef591a10 100644
--- a/crates/voicevox_core_c_api/src/compatible_engine.rs
+++ b/crates/voicevox_core_c_api/src/compatible_engine.rs
@@ -8,7 +8,10 @@ use std::{
 use libc::c_int;
 
 use tracing::warn;
-use voicevox_core::{StyleId, VoiceModelId, __internal::interop::PerformInference as _};
+use voicevox_core::{
+    StyleId, VoiceModelId,
+    __internal::interop::{PerformInference as _, ToJsonValue as _},
+};
 
 use crate::{helpers::display_error, init_logger_once};
 
@@ -218,16 +221,8 @@ pub extern "C" fn supported_devices() -> *const c_char {
     init_logger_once();
     return SUPPORTED_DEVICES.as_ptr();
 
-    static SUPPORTED_DEVICES: LazyLock<CString> = LazyLock::new(|| {
-        CString::new(
-            ONNXRUNTIME
-                .supported_devices()
-                .unwrap()
-                .to_json()
-                .to_string(),
-        )
-        .unwrap()
-    });
+    static SUPPORTED_DEVICES: LazyLock<CString> =
+        LazyLock::new(|| CString::new(ONNXRUNTIME.supported_devices().unwrap().to_json()).unwrap());
 }
 
 /// # Safety
diff --git a/crates/voicevox_core_c_api/src/lib.rs b/crates/voicevox_core_c_api/src/lib.rs
index 3019929cc..6c00ee218 100644
--- a/crates/voicevox_core_c_api/src/lib.rs
+++ b/crates/voicevox_core_c_api/src/lib.rs
@@ -38,6 +38,7 @@ use std::sync::Once;
 use tracing_subscriber::fmt::format::Writer;
 use tracing_subscriber::EnvFilter;
 use uuid::Uuid;
+use voicevox_core::__internal::interop::ToJsonValue as _;
 use voicevox_core::{AccentPhrase, AudioQuery, StyleId, UserDictWord};
 
 fn init_logger_once() {
@@ -703,8 +704,7 @@ pub unsafe extern "C" fn voicevox_onnxruntime_create_supported_devices_json(
 ) -> VoicevoxResultCode {
     init_logger_once();
     into_result_code_with_error((|| {
-        let supported_devices =
-            CString::new(onnxruntime.0.supported_devices()?.to_json().to_string()).unwrap();
+        let supported_devices = CString::new(onnxruntime.0.supported_devices()?.to_json()).unwrap();
         output_supported_devices_json.write_unaligned(
             C_STRING_DROP_CHECKER
                 .whitelist(supported_devices)
diff --git a/crates/voicevox_core_java_api/src/onnxruntime.rs b/crates/voicevox_core_java_api/src/onnxruntime.rs
index 2297fcdb6..3f1dfb5bd 100644
--- a/crates/voicevox_core_java_api/src/onnxruntime.rs
+++ b/crates/voicevox_core_java_api/src/onnxruntime.rs
@@ -6,6 +6,7 @@ use jni::{
     sys::jobject,
     JNIEnv,
 };
+use voicevox_core::__internal::interop::ToJsonValue as _;
 
 use crate::{common::throw_if_err, object};
 
@@ -56,7 +57,7 @@ unsafe extern "system" fn Java_jp_hiroshiba_voicevoxcore_blocking_Onnxruntime_rs
         )?;
         let devices = this.supported_devices()?;
 
-        assert!(match devices.to_json() {
+        assert!(match devices.to_json_value() {
             serde_json::Value::Object(o) => o.len() == 3, // `cpu`, `cuda`, `dml`
             _ => false,
         });
diff --git a/crates/voicevox_core_python_api/src/convert.rs b/crates/voicevox_core_python_api/src/convert.rs
index b71fc7468..ecbaf6a54 100644
--- a/crates/voicevox_core_python_api/src/convert.rs
+++ b/crates/voicevox_core_python_api/src/convert.rs
@@ -13,6 +13,7 @@ use serde_json::json;
 use uuid::Uuid;
 use voicevox_core::{
     AccelerationMode, AccentPhrase, AudioQuery, StyleId, SupportedDevices, VoiceModelMeta,
+    __internal::interop::ToJsonValue as _,
 };
 
 use crate::{
@@ -280,7 +281,7 @@ pub(crate) impl<T> voicevox_core::Result<T> {
 #[ext(SupportedDevicesExt)]
 impl SupportedDevices {
     pub(crate) fn to_py(self, py: Python<'_>) -> PyResult<&PyAny> {
-        assert!(match self.to_json() {
+        assert!(match self.to_json_value() {
             serde_json::Value::Object(o) => o.len() == 3, // `cpu`, `cuda`, `dml`
             _ => false,
         });