diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 65da307..d2f42c7 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -4,12 +4,24 @@ class ApplicationController < ActionController::Base
   # Only allow modern browsers supporting webp images, web push, badges, import maps, CSS nesting, and CSS :has.
   allow_browser versions: :modern
 
-  include SessionsHelper
-  before_action :check_logged_in
+  before_action :authenticate
+  helper_method :logged_in?, :current_user
 
-  def check_logged_in
-    return if current_user
+  private
 
-    redirect_to root_path
+  def logged_in?
+    !!current_user
+  end
+
+  def current_user
+    return unless session[:user_id]
+
+    @current_user ||= User.find(session[:user_id])
+  end
+
+  def authenticate
+    return if logged_in?
+
+    redirect_to root_path, alert: 'ログインしてください'
   end
 end
diff --git a/app/controllers/home_controller.rb b/app/controllers/home_controller.rb
index 0d073f6..5dc71da 100644
--- a/app/controllers/home_controller.rb
+++ b/app/controllers/home_controller.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class HomeController < ApplicationController
-  skip_before_action :check_logged_in, only: %i[index welcome terms privacy]
+  skip_before_action :authenticate, only: %i[index welcome terms privacy]
 
   def index
     redirect_to meal_plans_path if current_user.present?
diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index e8254db..84cb88b 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -1,13 +1,13 @@
 # frozen_string_literal: true
 
 class SessionsController < ApplicationController
-  skip_before_action :check_logged_in, only: :create
+  skip_before_action :authenticate, only: :create
 
   def create
     user = User.find_or_new_from_auth_hash(request.env['omniauth.auth'])
     user.find_or_new_family(request.env['omniauth.params']['invitation_token']) if user.family_id.nil?
     if user.save
-      log_in user
+      session[:user_id] = user.id
       redirect_to meal_plans_path, notice: 'ログインに成功しました'
     else
       redirect_to root_path, notice: 'ログインに失敗しました'
@@ -15,7 +15,7 @@ def create
   end
 
   def destroy
-    log_out
+    reset_session
     redirect_to root_path, notice: 'ログアウトしました'
   end
 end
diff --git a/app/helpers/sessions_helper.rb b/app/helpers/sessions_helper.rb
index 6917975..97aeb4c 100644
--- a/app/helpers/sessions_helper.rb
+++ b/app/helpers/sessions_helper.rb
@@ -1,18 +1,4 @@
 # frozen_string_literal: true
 
 module SessionsHelper
-  def current_user
-    return unless (user_id = session[:user_id])
-
-    @current_user ||= User.find_by(id: user_id)
-  end
-
-  def log_in(user)
-    session[:user_id] = user.id
-  end
-
-  def log_out
-    session.delete(:user_id)
-    remove_instance_variable(:@current_user)
-  end
 end
diff --git a/app/views/shared/_header.html.erb b/app/views/shared/_header.html.erb
index 1c6d9be..496b6e4 100644
--- a/app/views/shared/_header.html.erb
+++ b/app/views/shared/_header.html.erb
@@ -3,7 +3,7 @@
     <%= link_to image_tag('logo_small.png', class: 'h-11'), root_path %>
   </div>
   <div class="flex justify-between items-center">
-    <% if current_user %>
+    <% if logged_in? %>
       <%= link_to image_tag(current_user.icon, class: 'icon mx-2'), user_path %>
       <%= render 'shared/menu' %>
     <% end %>