diff --git a/app/models/comment/after_create_callback.rb b/app/models/comment/after_create_callback.rb
index eab7dc8f59f..6731d440278 100644
--- a/app/models/comment/after_create_callback.rb
+++ b/app/models/comment/after_create_callback.rb
@@ -76,8 +76,10 @@ def create_watch(comment)
   end
 
   def create_checker_id(comment)
+    return nil unless comment.user.mentor?
+
     product = comment.commentable
-    product.checker_id = comment.sender.id if product.checker_id.blank?
+    product.checker_id = comment.sender.id unless product.checker_id?
   end
 
   def delete_product_cache(product_id)
diff --git a/app/models/product.rb b/app/models/product.rb
index a2b10f2dbe5..1bfab3301b0 100644
--- a/app/models/product.rb
+++ b/app/models/product.rb
@@ -14,6 +14,7 @@ class Product < ApplicationRecord
 
   belongs_to :practice
   belongs_to :user, touch: true
+  belongs_to :checker, class_name: 'Product', optional: true
   alias sender user
 
   after_create ProductCallbacks.new
diff --git a/test/system/product/checker_test.rb b/test/system/product/checker_test.rb
new file mode 100644
index 00000000000..72a227df953
--- /dev/null
+++ b/test/system/product/checker_test.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'application_system_test_case'
+
+class Product::CheckerTest < ApplicationSystemTestCase
+  test 'be person on charge at comment on product of there are not person on charge' do
+    visit_with_auth '/products/unchecked?target=unchecked_no_replied', 'machida'
+    def assigned_product_count
+      text[/自分の担当 （(\d+)）/, 1].to_i
+    end
+
+    before_comment = assigned_product_count
+
+    [
+      '担当者がいない提出物の場合、担当者になる',
+      '自分が担当者の場合、担当者のまま'
+    ].each do |comment|
+      visit "/products/#{products(:product1).id}"
+      post_comment(comment)
+
+      visit '/products/unchecked?target=unchecked_no_replied'
+      assert_equal before_comment + 1, assigned_product_count
+    end
+  end
+
+  test 'be not person on charge at comment on product of there are person on charge' do
+    visit_with_auth '/products/unchecked?target=unchecked_no_replied', 'komagata'
+    product = find('.thread-list-item', match: :first)
+    product.click_button '担当する'
+    show_product_path = product.find_link(href: /products/)[:href]
+    logout
+
+    visit_with_auth '/products/unchecked?target=unchecked_no_replied', 'machida'
+
+    def assigned_product_count
+      text[/自分の担当 （(\d+)）/, 1].to_i
+    end
+
+    before_comment = assigned_product_count
+
+    visit show_product_path
+    post_comment('担当者がいる提出物の場合、担当者にならない')
+
+    visit '/products/unchecked?target=unchecked_no_replied'
+    assert_equal before_comment, assigned_product_count
+  end
+
+  test 'when student comment to a product, they are not in charge' do
+    old_product = products(:product8)
+
+    visit_with_auth product_url(old_product), 'kimura'
+
+    within first('#comments.loaded', wait: 10) do
+      fill_in 'new_comment[description]', with: 'edit test'
+      click_button 'コメントする'
+    end
+
+    assert_text 'コメントを投稿しました'
+    assert_nil Product.find(old_product.id).checker_id
+  end
+end
diff --git a/test/system/products_test.rb b/test/system/products_test.rb
index 96b64575050..4878487295e 100644
--- a/test/system/products_test.rb
+++ b/test/system/products_test.rb
@@ -353,48 +353,6 @@ class ProductsTest < ApplicationSystemTestCase
     assert_not page.has_css?('.pagination')
   end
 
-  test 'be person on charge at comment on product of there are not person on charge' do
-    visit_with_auth '/products/unchecked?target=unchecked_no_replied', 'machida'
-    def assigned_product_count
-      text[/自分の担当 （(\d+)）/, 1].to_i
-    end
-
-    before_comment = assigned_product_count
-
-    [
-      '担当者がいない提出物の場合、担当者になる',
-      '自分が担当者の場合、担当者のまま'
-    ].each do |comment|
-      visit "/products/#{products(:product1).id}"
-      post_comment(comment)
-
-      visit '/products/unchecked?target=unchecked_no_replied'
-      assert_equal before_comment + 1, assigned_product_count
-    end
-  end
-
-  test 'be not person on charge at comment on product of there are person on charge' do
-    visit_with_auth '/products/unchecked?target=unchecked_no_replied', 'komagata'
-    product = find('.thread-list-item', match: :first)
-    product.click_button '担当する'
-    show_product_path = product.find_link(href: /products/)[:href]
-    logout
-
-    visit_with_auth '/products/unchecked?target=unchecked_no_replied', 'machida'
-
-    def assigned_product_count
-      text[/自分の担当 （(\d+)）/, 1].to_i
-    end
-
-    before_comment = assigned_product_count
-
-    visit show_product_path
-    post_comment('担当者がいる提出物の場合、担当者にならない')
-
-    visit '/products/unchecked?target=unchecked_no_replied'
-    assert_equal before_comment, assigned_product_count
-  end
-
   test 'show user full_name next to user login_name' do
     visit_with_auth "/products/#{products(:product1).id}", 'kimura'
     assert_text 'mentormentaro (メンタ 麺太郎)'