diff --git a/src/Eccube/Form/Type/Shopping/OrderType.php b/src/Eccube/Form/Type/Shopping/OrderType.php
index 7409d9bd2b9..51944be4451 100644
--- a/src/Eccube/Form/Type/Shopping/OrderType.php
+++ b/src/Eccube/Form/Type/Shopping/OrderType.php
@@ -165,6 +165,19 @@ public function buildForm(FormBuilderInterface $builder, array $options)
             $charge = $Order->getPayment() ? $Order->getPayment()->getCharge() : 0;
             $Payments = $this->filterPayments($Payments, $Order->getPaymentTotal() - $charge);
 
+            // フォームから送信された支払方法が選択肢に存在するかどうか
+            // 選択肢に存在しなければ、選択肢の中で最初の支払方法を選択状態にする
+            $Payment = null;
+            if ($data['Payment']) {
+                $Payment = $this->paymentRepository->find($data['Payment']);
+            }
+            $Payment = !is_null($Payment) && in_array($Payment, $Payments, true) ?
+                $Payment : (current($Payments) ?: null);
+            if ( !is_null($Payment)) {
+                $data['Payment'] = (string)$Payment->getId();
+                $event->setData($data);
+            }
+
             $form = $event->getForm();
             $this->addPaymentForm($form, $Payments);
         });
diff --git a/src/Eccube/Resource/locale/messages.en.yaml b/src/Eccube/Resource/locale/messages.en.yaml
index 01fa5bca2ce..07cf6118480 100644
--- a/src/Eccube/Resource/locale/messages.en.yaml
+++ b/src/Eccube/Resource/locale/messages.en.yaml
@@ -1861,6 +1861,7 @@ purchase_flow.tax_rate_update: Tax Rate has been updated. Please confirm the tot
 purchase_flow.over_customer_point: You are not able to use points more than your current points.
 purchase_flow.over_payment_total: The points are more than the total amount.
 purchase_flow.over_stock: "%name% does not have enough stock."
+purchase_flow.payment_method_changed: "Payment method has been changed to %name% due to change in delivery method."
 
 #------------------------------------------------------------------------------------
 # Command
diff --git a/src/Eccube/Resource/locale/messages.ja.yaml b/src/Eccube/Resource/locale/messages.ja.yaml
index 9cf4b99c635..3c28e98838f 100644
--- a/src/Eccube/Resource/locale/messages.ja.yaml
+++ b/src/Eccube/Resource/locale/messages.ja.yaml
@@ -1862,6 +1862,7 @@ purchase_flow.tax_rate_update: 税率が更新されました。金額をご確
 purchase_flow.over_customer_point: 利用ポイントが所有ポイントを上回っています。
 purchase_flow.over_payment_total: 利用ポイントがお支払い金額を上回っています。
 purchase_flow.over_stock: "「%name%」の在庫が足りません。"
+purchase_flow.payment_method_changed: "配送方法の変更により支払方法が「%name%」に変更されました。"
 
 #------------------------------------------------------------------------------------
 # Command
diff --git a/src/Eccube/Service/PurchaseFlow/Processor/PaymentChangePostValidator.php b/src/Eccube/Service/PurchaseFlow/Processor/PaymentChangePostValidator.php
new file mode 100644
index 00000000000..d97a197ef85
--- /dev/null
+++ b/src/Eccube/Service/PurchaseFlow/Processor/PaymentChangePostValidator.php
@@ -0,0 +1,63 @@
+<?php
+
+/*
+ * This file is part of EC-CUBE
+ *
+ * Copyright(c) EC-CUBE CO.,LTD. All Rights Reserved.
+ *
+ * http://www.ec-cube.co.jp/
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Eccube\Service\PurchaseFlow\Processor;
+
+use Eccube\Entity\ItemHolderInterface;
+use Eccube\Entity\Order;
+use Eccube\Service\PurchaseFlow\ItemHolderPostValidator;
+use Eccube\Service\PurchaseFlow\PurchaseContext;
+use Symfony\Component\HttpFoundation\RequestStack;
+
+/**
+ * 配送方法変更により支払方法が変更されたかどうかを検知するバリデータ.
+ */
+class PaymentChangePostValidator extends ItemHolderPostValidator
+{
+    /**
+     * @var RequestStack
+     */
+    protected $requestStack;
+
+    /**
+     * PaymentChangePostValidator constructor.
+     *
+     * @param RequestStack $requestStack
+     */
+    public function __construct(RequestStack $requestStack)
+    {
+        $this->requestStack = $requestStack;
+    }
+
+    /**
+     * @param ItemHolderInterface $itemHolder
+     * @param PurchaseContext $context
+     */
+    public function validate(ItemHolderInterface $itemHolder, PurchaseContext $context)
+    {
+        /* @var Order $Order */
+        $Order = $itemHolder;
+        $request = $this->requestStack->getCurrentRequest();
+        $requestData = $request->request->all();
+
+        // 配送方法の変更によって選択していた支払方法が使用できなくなった場合、OrderTypeで支払方法が変更されている
+        if (isset($requestData['_shopping_order']['Payment'])) {
+
+            if (!is_null($Order->getPayment()) && $Order->getPayment()->getId() != $requestData['_shopping_order']['Payment']) {
+                if ($Order->getPayment()) {
+                    $this->throwInvalidItemException(trans('purchase_flow.payment_method_changed', ['%name%' => $Order->getPayment()->getMethod()]), null, true);
+                }
+            }
+        }
+    }
+}
diff --git a/tests/Eccube/Tests/Web/ShoppingControllerTest.php b/tests/Eccube/Tests/Web/ShoppingControllerTest.php
index c229becbfd3..82ca4b378e4 100644
--- a/tests/Eccube/Tests/Web/ShoppingControllerTest.php
+++ b/tests/Eccube/Tests/Web/ShoppingControllerTest.php
@@ -396,8 +396,10 @@ public function testPaymentWithError()
         ]);
 
         $this->assertTrue($this->client->getResponse()->isSuccessful());
-        $this->expected = 'お支払い方法を選択してください。';
-        $this->actual = $crawler->filter('p.ec-errorMessage')->text();
+
+        // 先頭の支払方法(郵便振替)が選択されていることを確認
+        $this->expected = '1';
+        $this->actual = $crawler->filter('input[name="_shopping_order[Payment]"]:checked')->attr('value');
         $this->verify();
     }