diff --git a/dictation_server/src/features/users/users.controller.ts b/dictation_server/src/features/users/users.controller.ts
index c9d6a56..cee1a78 100644
--- a/dictation_server/src/features/users/users.controller.ts
+++ b/dictation_server/src/features/users/users.controller.ts
@@ -662,8 +662,7 @@ export class UsersController {
     }
     const { userId } = decodedAccessToken as AccessToken;
     const context = makeContext(userId);
-    const userName = 'TEST';
-    //const userName = await this.usersService.getUserName(context, userId);
+    const userName = await this.usersService.getUserName(context, userId);
     return { userName };
   }
 }
diff --git a/dictation_server/src/features/users/users.service.spec.ts b/dictation_server/src/features/users/users.service.spec.ts
index 6c5c2b4..e749058 100644
--- a/dictation_server/src/features/users/users.service.spec.ts
+++ b/dictation_server/src/features/users/users.service.spec.ts
@@ -2624,3 +2624,45 @@ describe('UsersService.updateAcceptedVersion', () => {
     );
   });
 });
+
+describe('UsersService.getUserName', () => {
+  let source: DataSource | null = null;
+
+  beforeEach(async () => {
+    source = new DataSource({
+      type: 'sqlite',
+      database: ':memory:',
+      logging: false,
+      entities: [__dirname + '/../../**/*.entity{.ts,.js}'],
+      synchronize: true,
+    });
+    return source.initialize();
+  });
+
+  afterEach(async () => {
+    if (!source) return;
+    await source.destroy();
+    source = null;
+  });
+
+  it('ユーザーが存在しない場合は、ユーザー未存在エラー', async () => {
+    if (!source) fail();
+
+    try {
+      const module = await makeTestingModule(source);
+      if (!module) fail();
+      const context = makeContext(uuidv4());
+
+      const service = module.get<UsersService>(UsersService);
+      await service.getUserName(context, 'external_id');
+      fail();
+    } catch (e) {
+      if (e instanceof HttpException) {
+        expect(e.getStatus()).toEqual(HttpStatus.BAD_REQUEST);
+        expect(e.getResponse()).toEqual(makeErrorResponse('E010204'));
+      } else {
+        fail();
+      }
+    }
+  });
+});
diff --git a/dictation_server/src/features/users/users.service.ts b/dictation_server/src/features/users/users.service.ts
index 5ba3c84..66beb3c 100644
--- a/dictation_server/src/features/users/users.service.ts
+++ b/dictation_server/src/features/users/users.service.ts
@@ -4,7 +4,6 @@ import { makeErrorResponse } from '../../common/error/makeErrorResponse';
 import { isVerifyError, verify } from '../../common/jwt';
 import { getPublicKey } from '../../common/jwt/jwt';
 import { makePassword } from '../../common/password/password';
-import { AccessToken, IDToken } from '../../common/token';
 import {
   SortDirection,
   TaskListSortableAttribute,
@@ -1052,4 +1051,42 @@ export class UsersService {
       );
     }
   }
+  /**
+   * Azure AD B2Cからユーザー名を取得する
+   * @param context
+   * @param externalId
+   */
+  async getUserName(context: Context, externalId: string): Promise<string> {
+    this.logger.log(`[IN] [${context.trackingId}] ${this.getUserName.name}`);
+
+    try {
+      // extarnalIdの存在チェックを行う
+      await this.usersRepository.findUserByExternalId(externalId);
+      // ADB2Cからユーザー名を取得する
+      const adb2cUser = await this.adB2cService.getUser(externalId);
+      return adb2cUser.displayName;
+    } catch (e) {
+      this.logger.error(`error=${e}`);
+      if (e instanceof Error) {
+        switch (e.constructor) {
+          case UserNotFoundError:
+            throw new HttpException(
+              makeErrorResponse('E010204'),
+              HttpStatus.BAD_REQUEST,
+            );
+          default:
+            throw new HttpException(
+              makeErrorResponse('E009999'),
+              HttpStatus.INTERNAL_SERVER_ERROR,
+            );
+        }
+      }
+      throw new HttpException(
+        makeErrorResponse('E009999'),
+        HttpStatus.INTERNAL_SERVER_ERROR,
+      );
+    } finally {
+      this.logger.log(`[OUT] [${context.trackingId}] ${this.getUserName.name}`);
+    }
+  }
 }