diff --git a/views/includes/header.php b/views/includes/header.php
index 87c1537..bec8749 100644
--- a/views/includes/header.php
+++ b/views/includes/header.php
@@ -2,6 +2,7 @@
 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="ja">
   <head>
     <meta content="text/html; charset=utf-8" http-equiv="content-type" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
     <title><?php echo $title; ?></title>
     <link rel="stylesheet" type="text/css" href="/static/style.css" />
     <style>
