diff --git a/index.html b/index.html
index 3d637b6..bcf1d46 100644
--- a/index.html
+++ b/index.html
@@ -304,6 +304,15 @@ <h3>💡 ヒント</h3>
     <script type="module" src="js/error-handler.js"></script>
     <script type="module" src="js/notification-system.js"></script>
     <script type="module" src="js/main.js"></script>
+    <!-- Google tag (gtag.js) -->
+    <script async src="https://www.googletagmanager.com/gtag/js?id=G-NR5GY7P75K"></script>
+    <script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+
+    gtag('config', 'G-NR5GY7P75K');
+    </script>
 </body>
 
 </html>
\ No newline at end of file