diff --git a/app/controllers/tickets_controller.rb b/app/controllers/tickets_controller.rb
index 30b6e6f5..c53336a0 100644
--- a/app/controllers/tickets_controller.rb
+++ b/app/controllers/tickets_controller.rb
@@ -45,5 +45,10 @@ def ticket_update_params
 
   def load_ticket
     @ticket = Ticket.find(params[:id])
+
+    unless @ticket.exited_gate.nil?
+      flash[:error] = "降車済みの切符です。"
+      redirect_to root_path
+    end
   end
 end
diff --git a/app/models/gate.rb b/app/models/gate.rb
index 6fbdb509..a4ddf96c 100644
--- a/app/models/gate.rb
+++ b/app/models/gate.rb
@@ -7,7 +7,18 @@ class Gate < ApplicationRecord
 
   scope :order_by_station_number, -> { order(:station_number) }
 
+  # 当駅で降りられる？
   def exit?(ticket)
-    true
+    # 乗車駅～降車駅（当駅）間の区間数 ※station_numberの差＝区間数
+    traveled = (ticket.entered_gate.station_number - self.station_number).abs
+
+    # 同じ駅では降りられない
+    return false if traveled == 0
+
+    # 区間数から所要運賃を算出 ※traveledが範囲外であることは想定しない
+    required_fare = FARES[traveled - 1]
+
+    # 切符の額面が所要運賃以上なら降りられる
+    required_fare <= ticket.fare
   end
 end
diff --git a/app/models/ticket.rb b/app/models/ticket.rb
index eac5d011..e2ff48fd 100644
--- a/app/models/ticket.rb
+++ b/app/models/ticket.rb
@@ -3,4 +3,15 @@ class Ticket < ApplicationRecord
   belongs_to :exited_gate, class_name: 'Gate', foreign_key: 'exited_gate_id', required: false
   validates :fare, presence: true, inclusion: Gate::FARES
   validates :entered_gate_id, presence: true
+  validate :exited_gate_id_validation
+
+
+  # カスタムvalidation: exited_gate_idの駅で降りられるか？
+  def exited_gate_id_validation
+    return if exited_gate_id.nil?   # 降車駅が指定されていない場合（≒create直後）はスルーする
+
+    unless exited_gate.exit?(self)
+      errors.add(:exited_gate, "では降車できません。")
+    end
+  end
 end
diff --git a/test/models/gate_test.rb b/test/models/gate_test.rb
index e6f39cd6..53b94569 100644
--- a/test/models/gate_test.rb
+++ b/test/models/gate_test.rb
@@ -19,7 +19,6 @@ class GateTest < ActiveSupport::TestCase
   end
 
   test 'うめだで150円の切符を買って、みくにで降りる（運賃不足）' do
-    skip 'Please implement this!'
     ticket = Ticket.create!(fare: 150, entered_gate: @umeda)
     refute @mikuni.exit?(ticket)
   end
@@ -46,7 +45,6 @@ class GateTest < ActiveSupport::TestCase
   end
 
   test 'みくにで150円の切符を買って、うめだで降りる（運賃不足）' do
-    skip 'Please implement this!'
     ticket = Ticket.create!(fare: 150, entered_gate: @mikuni)
     refute @umeda.exit?(ticket)
   end
@@ -63,7 +61,6 @@ class GateTest < ActiveSupport::TestCase
 
   # その他
   test '同じ駅では降りられない' do
-    skip 'Please implement this!'
     ticket = Ticket.create!(fare: 190, entered_gate: @umeda)
     refute @umeda.exit?(ticket)
 
diff --git a/test/system/tickets_test.rb b/test/system/tickets_test.rb
index 64c7bdc6..fa7befd6 100644
--- a/test/system/tickets_test.rb
+++ b/test/system/tickets_test.rb
@@ -14,7 +14,6 @@ class TicketsTest < ApplicationSystemTestCase
   end
 
   test '運賃が足りない場合' do
-    skip 'Please implement this!'
     visit root_path
     select '150円', from: '切符'
     select 'うめだ', from: '乗車駅'
@@ -27,7 +26,6 @@ class TicketsTest < ApplicationSystemTestCase
   end
 
   test '同じ駅で降りる場合' do
-    skip 'Please implement this!'
     visit root_path
     select '150円', from: '切符'
     select 'うめだ', from: '乗車駅'
@@ -40,7 +38,6 @@ class TicketsTest < ApplicationSystemTestCase
   end
 
   test 'すでに使用済みの切符を指定されたらトップページに移動する' do
-    skip 'Please implement this!'
     # edit
     ticket = Ticket.create!(fare: 150, entered_gate: gates(:umeda), exited_gate: gates(:juso))
     visit edit_ticket_path(ticket)