diff --git a/.eleventy.js b/.eleventy.js
index 1e878bc7ed2b..8996d837ae30 100644
--- a/.eleventy.js
+++ b/.eleventy.js
@@ -44,7 +44,7 @@ const imageShortcode = async (src, alt, pathPrefix = '') => {
   } catch (e) {
     // エラーが起きたら代替画像にする
     console.log('[image-short-code] error', src);
-    return `<img src='${pathPrefix}images/alternate-feed-image.png' alt='${alt}' loading='lazy' decoding='async' width='256' height='256'>`
+    return `<img src='${pathPrefix}images/alternate-feed-image.png' alt='${alt}' loading='lazy' width='256' height='256'>`
   }
 
   return Image.generateHTML(metadata, {
diff --git a/src/site/_includes/layouts/main.njk b/src/site/_includes/layouts/main.njk
index f917929c0d18..2c6ad68166ad 100644
--- a/src/site/_includes/layouts/main.njk
+++ b/src/site/_includes/layouts/main.njk
@@ -65,11 +65,11 @@
         <div class="ui-layout-container">
             <div class="ui-section-header__layout ui-layout-flex">
                 <a href="{{ constants.siteUrl }}" role="link" aria-label="#">
-                    <img src="{{ page.url | relativeUrl }}images/icon.png" alt='サイトロゴ' loading="lazy" decoding='async' width='96' height='96' />
+                    <img src="{{ page.url | relativeUrl }}images/icon.png" alt='サイトロゴ' loading="eager" width='96' height='96' />
                     <span class='ui-section-header__title'>{{ constants.siteTitle }}</span>
                 </a>
                 <a href="{{ constants.gitHubRepositoryUrl }}" role="link" aria-label="#">
-                    <img src='{{ page.url | relativeUrl }}images/github-mark.png' alt='GitHubロゴ' loading="lazy" decoding='async' width='96' height='96' />
+                    <img src='{{ page.url | relativeUrl }}images/github-mark.png' alt='GitHubロゴ' loading="eager" width='96' height='96' />
                 </a>
             </div>
         </div>
diff --git a/src/site/_includes/layouts/partials/feed-item.njk b/src/site/_includes/layouts/partials/feed-item.njk
index 3db6f1e58e26..e04e18ce8ade 100644
--- a/src/site/_includes/layouts/partials/feed-item.njk
+++ b/src/site/_includes/layouts/partials/feed-item.njk
@@ -3,14 +3,14 @@
         {% if feedItem.image %}
             {% image feedItem.image.url, '記事のアイキャッチ画像', page.url | relativeUrl %}
         {% else %}
-            <img src='{{ page.url | relativeUrl }}images/alternate-feed-image.png' loading="lazy" decoding='async' alt='記事のアイキャッチ画像' width='256' height='256'>
+            <img src='{{ page.url | relativeUrl }}images/alternate-feed-image.png' loading="lazy" alt='記事のアイキャッチ画像' width='256' height='256'>
         {% endif %}
     </a>
     <div class='ui-feed-item__content'>
         <a class='ui-feed-item__title' href='{{ feedItem.url }}'>{{ feedItem._custom.originalTitle }}</a>
         {% if feedItem._custom.hatenaCount > 0 %}
             <div class='ui-feed-item__hatena-count' title='はてなブックマーク数'>
-                <img src='{{ page.url | relativeUrl }}images/hatenabookmark-icon.png' alt='はてなブックマークアイコン' loading="lazy" decoding='async' width='96' height='96'>
+                <img src='{{ page.url | relativeUrl }}images/hatenabookmark-icon.png' alt='はてなブックマークアイコン' loading="lazy" width='96' height='96'>
                 <span>{{ feedItem._custom.hatenaCount }}</span>
             </div>
         {% endif %}
diff --git a/src/site/_includes/layouts/partials/top-section.njk b/src/site/_includes/layouts/partials/top-section.njk
index 4ab53a4168f6..8b4754969dc7 100644
--- a/src/site/_includes/layouts/partials/top-section.njk
+++ b/src/site/_includes/layouts/partials/top-section.njk
@@ -7,7 +7,7 @@
             <div class="ui-component-cta ui-layout-flex">
                 <form class="ui-component-form ui-layout-grid">
                     <label class='ui-component-form__label' for='feed-url-slack'>
-                        <img src='{{ page.url | relativeUrl }}images/slack-mark.png' alt='Slackのロゴ' loading="lazy" decoding='async' width='96' height='96'>
+                        <img src='{{ page.url | relativeUrl }}images/slack-mark.png' alt='Slackのロゴ' loading="eager" width='96' height='96'>
                     </label>
                     <input type='text' id='feed-url-slack' class="ui-component-input ui-component-input-medium" readonly value='/feed {{ constants.feedUrls.rss }}'>
                     <button type="button" class="ui-component-button ui-component-button-medium ui-component-button-primary feed-url-copy-button">コピー</button>
@@ -22,10 +22,10 @@
                 </form>
                 <div class='ui-top-section__subscribe'>
                     <a href='https://feedly.com/i/subscription/feed/{{ constants.feedUrls.rss }}' target="_blank" rel="noopener">
-                        <img src='{{ page.url | relativeUrl }}images/subscribe-feedly.png' alt='follow us in feedly' width='152' height='56'>
+                        <img src='{{ page.url | relativeUrl }}images/subscribe-feedly.png' loading="eager" alt='follow us in feedly' width='152' height='56'>
                     </a>
                     <a href="https://www.inoreader.com?add_feed={{ constants.feedUrls.rss }}" target="_blank" rel="noopener">
-                        <img src="{{ page.url | relativeUrl }}images/subscribe-inoreader.png" alt="follow us in inoreader" width='260' height='72'>
+                        <img src="{{ page.url | relativeUrl }}images/subscribe-inoreader.png" loading="eager" alt="follow us in inoreader" width='260' height='72'>
                     </a>
                 </div>
             </div>
diff --git a/src/site/blog-feed.njk b/src/site/blog-feed.njk
index c48db85dc12e..48d9448c5174 100644
--- a/src/site/blog-feed.njk
+++ b/src/site/blog-feed.njk
@@ -31,14 +31,14 @@ permalink: "blogs/{{ blogFeed.linkMd5Hash }}/"
                         {% if feedItem.ogImageUrl %}
                             {% image feedItem.ogImageUrl, '記事のアイキャッチ画像', page.url | relativeUrl %}
                         {% else %}
-                            <img src='{{ page.url | relativeUrl }}images/alternate-feed-image.png' loading="lazy" decoding='async' alt='記事のアイキャッチ画像' width='256' height='256'>
+                            <img src='{{ page.url | relativeUrl }}images/alternate-feed-image.png' loading="lazy" alt='記事のアイキャッチ画像' width='256' height='256'>
                         {% endif %}
                     </a>
                     <div class='ui-feed-item__content'>
                         <a class='ui-feed-item__title' href='{{ feedItem.link }}'>{{ feedItem.title }}</a>
                         {% if feedItem.hatenaCount > 0 %}
                             <div class='ui-feed-item__hatena-count' title='はてなブックマーク数'>
-                                <img src='{{ page.url | relativeUrl }}images/hatenabookmark-icon.png' alt='はてなブックマークアイコン' loading="lazy" decoding='async' width='96' height='96'>
+                                <img src='{{ page.url | relativeUrl }}images/hatenabookmark-icon.png' alt='はてなブックマークアイコン' loading="lazy" width='96' height='96'>
                                 <span>{{ feedItem.hatenaCount }}</span>
                             </div>
                         {% endif %}
diff --git a/src/site/blogs.njk b/src/site/blogs.njk
index bcf14fc78bcb..cb33ad731021 100644
--- a/src/site/blogs.njk
+++ b/src/site/blogs.njk
@@ -17,7 +17,7 @@ eleventyComputed:
                         {% if blogFeed.ogImageUrl %}
                             {% image blogFeed.ogImageUrl, 'ブログのアイキャッチ画像', '../' %}
                         {% else %}
-                            <img src='{{ page.url | relativeUrl }}images/alternate-feed-image.png' loading="lazy" decoding='async' alt='記事のアイキャッチ画像' width='256' height='256'>
+                            <img src='{{ page.url | relativeUrl }}images/alternate-feed-image.png' loading="lazy" alt='記事のアイキャッチ画像' width='256' height='256'>
                         {% endif %}
                     </a>
                     <div class='ui-blog__content'>