diff --git a/src/entry/adaptor/errors.test.ts b/src/entry/adaptor/errors.test.ts
new file mode 100644
index 0000000..d91cedf
--- /dev/null
+++ b/src/entry/adaptor/errors.test.ts
@@ -0,0 +1,33 @@
+import { describe, it, expect } from 'vitest';
+
+describe('正しくエラーコードに変換できる', () => {
+  const errorToCode = (error: Error) => {
+    switch (error.message) {
+      case 'too many members':
+        return 'TOO_MANY_MEMBERS';
+      case 'no member':
+        return 'NO_MEMBER';
+      case 'teamName Exists':
+        return 'TEAM_ALREADY_EXISTS';
+      default:
+        return 'UNKNOWN_ERROR';
+    }
+  };
+  it('too many members', () => {
+    const error = new Error('too many members');
+    expect(errorToCode(error)).toBe('TOO_MANY_MEMBERS');
+  });
+  it('no member', () => {
+    const error = new Error('no member');
+    expect(errorToCode(error)).toBe('NO_MEMBER');
+  });
+  it('teamName Exists', () => {
+    const error = new Error('teamName Exists');
+    expect(errorToCode(error)).toBe('TEAM_ALREADY_EXISTS');
+  });
+
+  it('other', () => {
+    const error = new Error('other');
+    expect(errorToCode(error)).toBe('UNKNOWN_ERROR');
+  });
+});
diff --git a/src/entry/adaptor/errors.ts b/src/entry/adaptor/errors.ts
new file mode 100644
index 0000000..9c29595
--- /dev/null
+++ b/src/entry/adaptor/errors.ts
@@ -0,0 +1,12 @@
+export function errorToCode(error: Error): string {
+  switch (error.message) {
+    case 'too many members':
+      return 'TOO_MANY_MEMBERS';
+    case 'no member':
+      return 'NO_MEMBER';
+    case 'teamName Exists':
+      return 'TEAM_ALREADY_EXISTS';
+    default:
+      return 'UNKNOWN_ERROR';
+  }
+}
diff --git a/src/entry/main.ts b/src/entry/main.ts
index 06e4351..4017c57 100644
--- a/src/entry/main.ts
+++ b/src/entry/main.ts
@@ -4,6 +4,7 @@ import { entryRequestSchema } from './schema.js';
 import { Controller } from './controller.js';
 import { Option, Result } from '@mikuroxina/mini-fn';
 import { JSONEntryRepository } from './adaptor/json.js';
+import { errorToCode } from './adaptor/errors.js';
 
 export const entryHandler = new Hono();
 // export const controller = new Controller(new DummyRepository());
@@ -19,7 +20,7 @@ entryHandler.post('/', zValidator('json', entryRequestSchema), async (c) => {
     category,
   });
   if (Result.isErr(res)) {
-    return c.json({ error: res[1].message }, 400);
+    return c.json({ error: errorToCode(res[1]) }, 400);
   }
 
   return c.json({
@@ -34,7 +35,7 @@ entryHandler.post('/', zValidator('json', entryRequestSchema), async (c) => {
 entryHandler.get('/', async (c) => {
   const res = await controller.get();
   if (Result.isErr(res)) {
-    return c.json({ error: res[1].message }, 400);
+    return c.json({ error: errorToCode(res[1]) }, 400);
   }
 
   return c.json([...res[1]]);
diff --git a/tsconfig.json b/tsconfig.json
index f19fa69..1f9543f 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -19,7 +19,7 @@
     "moduleResolution": "Node16",
     "esModuleInterop": true,
     "forceConsistentCasingInFileNames": true,
-    "pretty": true
+    "pretty": true,
   },
   "include": ["**/*.ts"],
   "exclude": ["node_modules"]