diff --git a/.env.example b/.env.example
index 06c004b..84e517d 100644
--- a/.env.example
+++ b/.env.example
@@ -36,5 +36,7 @@ PUSHER_APP_ID=
 PUSHER_APP_KEY=
 PUSHER_APP_SECRET=
 
+# (Optional) reCAPTCHA Key
+# https://www.google.com/recaptcha
 NOCAPTCHA_SECRET=
-NOCAPTCHA_SITEKEY=
\ No newline at end of file
+NOCAPTCHA_SITEKEY=
diff --git a/app/Http/Controllers/Auth/RegisterController.php b/app/Http/Controllers/Auth/RegisterController.php
index d3052d1..0e79f03 100644
--- a/app/Http/Controllers/Auth/RegisterController.php
+++ b/app/Http/Controllers/Auth/RegisterController.php
@@ -47,12 +47,18 @@ class RegisterController extends Controller
      */
     protected function validator(array $data)
     {
-        return Validator::make($data, [
+        $rules = [
             'name' => 'required|string|regex:/^[a-zA-Z0-9_-]+$/u|max:15|unique:users',
             'email' => 'required|string|email|max:255|unique:users',
-            'password' => 'required|string|min:6|confirmed',
-            'g-recaptcha-response' => 'required|captcha'
-            ],
+            'password' => 'required|string|min:6|confirmed'
+        ];
+
+        // reCAPTCHAのキーが設定されている場合、判定を有効化
+        if (!empty(config('captcha.secret'))) {
+            $rules['g-recaptcha-response'] = 'required|captcha';
+        }
+
+        return Validator::make($data, $rules,
             ['name.regex' => 'ユーザー名には半角英数字とアンダーバー、ハイフンのみ使用できます。'],
             ['name' => 'ユーザー名']
         );
diff --git a/resources/views/auth/register.blade.php b/resources/views/auth/register.blade.php
index 59b2fa9..ff9fc34 100644
--- a/resources/views/auth/register.blade.php
+++ b/resources/views/auth/register.blade.php
@@ -3,7 +3,9 @@
 @section('title', '新規登録')
 
 @push('head')
-    {!! NoCaptcha::renderJs() !!}
+    @if (!empty(config('captcha.secret')))
+        {!! NoCaptcha::renderJs() !!}
+    @endif
 @endpush
 
 @section('content')
@@ -57,14 +59,16 @@
                         </div>
                     </div>
                 </div>
-                <div class="form-row ml-1 mt-2 my-4">
-                    <div class="mx-auto">
-                        {!! NoCaptcha::display() !!}
+                @if (!empty(config('captcha.secret')))
+                    <div class="form-row ml-1 mt-2 my-4">
+                        <div class="mx-auto">
+                            {!! NoCaptcha::display() !!}
+                        </div>
+                        @if ($errors->has('g-recaptcha-response'))
+                            <div class="invalid-feedback d-block text-center">{{ $errors->first('g-recaptcha-response') }}</div>
+                        @endif
                     </div>
-                    @if ($errors->has('g-recaptcha-response'))
-                        <div class="invalid-feedback d-block text-center">{{ $errors->first('g-recaptcha-response') }}</div>
-                    @endif
-                </div>
+                @endif
 
                 <div class="text-center">
                     <button class="btn btn-primary btn-lg" type="submit">登録</button>