diff --git a/app/helpers/image_helper.rb b/app/helpers/image_helper.rb
new file mode 100644
index 0000000..9b6afd7
--- /dev/null
+++ b/app/helpers/image_helper.rb
@@ -0,0 +1,16 @@
+module ImageHelper
+  # 画像圧縮オプション（品質85%で視覚的な劣化なく30-50%削減）
+  IMAGE_COMPRESSION_OPTIONS = { saver: { quality: 85 } }.freeze
+
+  # variantオプションに圧縮設定をマージ
+  #
+  # @param options [Hash] resize_to_fillなどのvariantオプション
+  # @return [Hash] 圧縮設定がマージされたオプション
+  #
+  # @example
+  #   compressed_variant(resize_to_fill: [450, 300])
+  #   # => { resize_to_fill: [450, 300], saver: { quality: 85 } }
+  def compressed_variant(options)
+    options.merge(IMAGE_COMPRESSION_OPTIONS)
+  end
+end
diff --git a/app/views/shared/_membership_avatar.html.erb b/app/views/shared/_membership_avatar.html.erb
index ce739af..af5d43e 100644
--- a/app/views/shared/_membership_avatar.html.erb
+++ b/app/views/shared/_membership_avatar.html.erb
@@ -1,9 +1,10 @@
 <% size ||= 60 %>
 <% initial_font_size ||= 'sm' %>
+<% lazy ||= true %>
 
 <% if membership.avatar.attached? %>
   <div style="width: <%= size %>px; height: <%= size %>px;" class="mx-auto rounded-full bg-gray-200">
-    <%= image_tag membership.avatar.variant(resize_to_fill: [size, size]), alt: "#{membership.display_name}のアバター", class: "w-#{size/4} h-#{size/4} rounded-full object-cover" %>
+    <%= image_tag membership.avatar.variant(compressed_variant(resize_to_fill: [size, size])), alt: "#{membership.display_name}のアバター", class: "w-#{size/4} h-#{size/4} rounded-full object-cover", loading: lazy ? "lazy" : "eager" %>
   </div>
 <% else %>
   <div style="width: <%= size %>px; height: <%= size %>px;" class="mx-auto rounded-full bg-gray-500 flex items-center justify-center text-white">
diff --git a/app/views/teams/events/_main_column.html.erb b/app/views/teams/events/_main_column.html.erb
index 9c081dd..b171714 100644
--- a/app/views/teams/events/_main_column.html.erb
+++ b/app/views/teams/events/_main_column.html.erb
@@ -25,7 +25,7 @@
 
   <% if event.image.attached? %>
     <div class="aspect-[3/2] mb-6 bg-gray-200">
-      <%= image_tag event.image.variant(resize_to_fill: [1500, 1000]), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover" %>
+      <%= image_tag event.image.variant(compressed_variant(resize_to_fill: [1500, 1000])), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover" %>
     </div>
   <% else %>
     <div class="aspect-[3/2] mb-6 bg-gray-300 flex items-center justify-center text-white">
@@ -127,7 +127,7 @@
     <div data-tabs-target="panel" data-tab="report" class="<%= event.report_available? ? '' : 'hidden' %> py-6">
       <% if event.report_image.attached? %>
         <div class="aspect-[3/2] mb-6 bg-gray-200">
-          <%= image_tag event.report_image.variant(resize_to_fill: [1500, 1000]), alt: "#{event.name}の開催レポート画像", class: "w-full h-full object-cover" %>
+          <%= image_tag event.report_image.variant(compressed_variant(resize_to_fill: [1500, 1000])), alt: "#{event.name}の開催レポート画像", class: "w-full h-full object-cover", loading: "lazy" %>
         </div>
       <% end %>
 
diff --git a/app/views/teams/memberships/_event_item.html.erb b/app/views/teams/memberships/_event_item.html.erb
index 5b88b4d..e423382 100644
--- a/app/views/teams/memberships/_event_item.html.erb
+++ b/app/views/teams/memberships/_event_item.html.erb
@@ -1,7 +1,7 @@
 <%= link_to team_event_path(@team, event), class: "flex gap-4 py-4 border-t border-gray-200" do %>
   <div class="w-[120px] md:w-[150px] h-[80px] md:h-[100px] bg-gray-200 relative flex-shrink-0">
     <% if event.image.attached? %>
-        <%= image_tag event.image.variant(resize_to_fill: [150, 100]), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover" %>
+        <%= image_tag event.image.variant(compressed_variant(resize_to_fill: [150, 100])), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover", loading: "lazy" %>
     <% else %>
       <div class="aspect-[3/2] bg-gray-500 flex items-center justify-center text-white">
         <span class="text-xs md:text-md">No Image</span>
diff --git a/app/views/teams/show.html.erb b/app/views/teams/show.html.erb
index f8b37cc..551de18 100644
--- a/app/views/teams/show.html.erb
+++ b/app/views/teams/show.html.erb
@@ -16,7 +16,7 @@
             <div class="aspect-[3/2] bg-gray-200 relative">
               <% if event.image.attached? %>
                 <div class="aspect-[3/2] mb-3 bg-gray-200">
-                  <%= image_tag event.image.variant(resize_to_fill: [450, 300]), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover" %>
+                  <%= image_tag event.image.variant(compressed_variant(resize_to_fill: [450, 300])), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover", loading: "lazy" %>
                 </div>
               <% else %>
                 <div class="aspect-[3/2] mb-3 bg-gray-500 flex items-center justify-center text-white">
@@ -167,7 +167,7 @@
           <div class="aspect-[3/2] bg-gray-200 relative">
             <% if event.image.attached? %>
               <div class="aspect-[3/2] mb-3 bg-gray-200">
-                <%= image_tag event.image.variant(resize_to_fill: [450, 300]), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover" %>
+                <%= image_tag event.image.variant(compressed_variant(resize_to_fill: [450, 300])), alt: "#{event.name}のイメージ画像", class: "w-full h-full object-cover", loading: "lazy" %>
               </div>
             <% else %>
               <div class="aspect-[3/2] mb-3 bg-gray-500 flex items-center justify-center text-white">
diff --git a/spec/helpers/image_helper_spec.rb b/spec/helpers/image_helper_spec.rb
new file mode 100644
index 0000000..b24e926
--- /dev/null
+++ b/spec/helpers/image_helper_spec.rb
@@ -0,0 +1,20 @@
+require 'rails_helper'
+
+RSpec.describe ImageHelper, type: :helper do
+  describe '#compressed_variant' do
+    it '圧縮オプションをマージして返す' do
+      result = helper.compressed_variant(resize_to_fill: [ 450, 300 ])
+      expect(result).to eq(resize_to_fill: [ 450, 300 ], saver: { quality: 85 })
+    end
+
+    it '既存のオプションを保持しつつ圧縮オプションを追加する' do
+      result = helper.compressed_variant(resize_to_limit: [ 1000, 1000 ], format: :webp)
+      expect(result).to eq(resize_to_limit: [ 1000, 1000 ], format: :webp, saver: { quality: 85 })
+    end
+
+    it '空のハッシュにも圧縮オプションを追加する' do
+      result = helper.compressed_variant({})
+      expect(result).to eq(saver: { quality: 85 })
+    end
+  end
+end