diff --git a/plugins/bc-front/templates/plugin/BcMail/element/mail_input.php b/plugins/bc-front/templates/plugin/BcMail/element/mail_input.php
index a1dca16235..7a6610a4f8 100755
--- a/plugins/bc-front/templates/plugin/BcMail/element/mail_input.php
+++ b/plugins/bc-front/templates/plugin/BcMail/element/mail_input.php
@@ -95,7 +95,7 @@
 			}
 
 			/* 説明欄 */
-			$isGroupValidComplate = in_array('VALID_GROUP_COMPLATE', explode(',', $field->valid_ex));
+			$isGroupValidComplate = in_array('VALID_GROUP_COMPLATE', explode(',', (string) $field->valid_ex));
 			if(!$isGroupValidComplate) {
 				echo $this->BcBaser->mailFormError("MailMessage." . $field->field_name);
 			}
diff --git a/plugins/bc-mail/src/Controller/MailController.php b/plugins/bc-mail/src/Controller/MailController.php
index 1efcc57fbe..06860febc7 100755
--- a/plugins/bc-mail/src/Controller/MailController.php
+++ b/plugins/bc-mail/src/Controller/MailController.php
@@ -281,7 +281,7 @@ public function submit(
             $entity = $mailMessagesService->create($mailContent, $this->getRequest()->getData());
         } catch (PersistenceFailedException $e) {
             $entity = $e->getEntity();
-            $mailMessage->auth_captcha = '';
+            $entity->auth_captcha = '';
             $this->BcMessage->setError(__d('baser_core', '入力内容を確認し、再度送信してください。'));
             $this->set($service->getViewVarsForConfirm($mailContent, $entity));
             return $this->render($service->getConfirmTemplate($mailContent));
diff --git a/plugins/bc-mail/src/Model/Table/MailMessagesTable.php b/plugins/bc-mail/src/Model/Table/MailMessagesTable.php
index 209b58d903..e4b3c1158a 100755
--- a/plugins/bc-mail/src/Model/Table/MailMessagesTable.php
+++ b/plugins/bc-mail/src/Model/Table/MailMessagesTable.php
@@ -252,7 +252,7 @@ protected function setupValidate(array $postData)
 
             // ### 拡張バリデーション
             if ($mailField->valid_ex && !empty($mailField->use_field)) {
-                $valids = explode(',', $mailField->valid_ex);
+                $valids = explode(',', (string) $mailField->valid_ex);
                 foreach($valids as $valid) {
                     $options = preg_split('/(?<!\\\)\|/', $mailField->options);
                     /**
@@ -449,7 +449,7 @@ protected function _validGroupComplete(EntityInterface $entity)
         $dists = [];
         foreach($this->mailFields as $mailField) {
             // 対象フィールドがあれば、バリデートグループごとに配列に格納する
-            $valids = explode(',', $mailField->valid_ex);
+            $valids = explode(',', (string) $mailField->valid_ex);
             if (in_array('VALID_GROUP_COMPLATE', $valids)) {
                 $dists[$mailField->group_valid][] = [
                     'name' => $mailField->field_name,
@@ -522,9 +522,9 @@ public function convertDatasToMail($data, $options)
 
         foreach($mailFields as $key => $value) {
             $fieldName = $value->field_name;
-            $value->before_attachment = strip_tags($value->before_attachment);
-            $value->after_attachment = str_replace(["<br />", "<br>"], "\n", strip_tags($value->after_attachment, "<br>"));
-            $value->head = str_replace(["<br />", "<br>"], "", strip_tags($value->head, "<br>"));
+            $value->before_attachment = strip_tags((string) $value->before_attachment);
+            $value->after_attachment = str_replace(["<br />", "<br>"], "\n", strip_tags((string) $value->after_attachment, "<br>"));
+            $value->head = str_replace(["<br />", "<br>"], "", strip_tags((string) $value->head, "<br>"));
             if ($value->no_send) {
                 unset($message->{$fieldName});
             }
diff --git a/plugins/bc-mail/src/Service/Admin/MailFieldsAdminService.php b/plugins/bc-mail/src/Service/Admin/MailFieldsAdminService.php
index 90380721cd..158a5a897e 100644
--- a/plugins/bc-mail/src/Service/Admin/MailFieldsAdminService.php
+++ b/plugins/bc-mail/src/Service/Admin/MailFieldsAdminService.php
@@ -88,7 +88,7 @@ public function getViewVarsForEdit(int $mailContentId, EntityInterface $mailFiel
     {
         /* @var \BcMail\Service\MailContentsService $mailContentsService */
         $mailContentsService = $this->getService(MailContentsServiceInterface::class);
-        $mailField->valid_ex = explode(',', $mailField->valid_ex);
+        $mailField->valid_ex = explode(',', (string) $mailField->valid_ex);
         $mailContent = $mailContentsService->get($mailContentId);
         return [
             'mailContent' => $mailContent,
diff --git a/plugins/bc-mail/tests/TestCase/Controller/MailControllerTest.php b/plugins/bc-mail/tests/TestCase/Controller/MailControllerTest.php
index c63052b3f3..c9bc5c15fa 100644
--- a/plugins/bc-mail/tests/TestCase/Controller/MailControllerTest.php
+++ b/plugins/bc-mail/tests/TestCase/Controller/MailControllerTest.php
@@ -151,7 +151,6 @@ public function testConfirm()
      */
     public function testSubmit()
     {
-        $this->markTestIncomplete('このテストは未確認です');
         //準備
         $this->enableSecurityToken();
         $this->enableCsrfToken();
@@ -159,7 +158,8 @@ public function testSubmit()
         SiteConfigFactory::make(['name' => 'email', 'value' => 'abc@gmail.com'])->persist();
         SiteConfigFactory::make(['name' => 'admin-theme', 'value' => 'test theme'])->persist();
         SiteFactory::make(['id' => 1])->persist();
-        MailFieldsFactory::make(['mail_content_id' => 1, 'field_name' => 'sex'])->persist();
+        MailFieldsFactory::make(['mail_content_id' => 1, 'field_name' => 'sex', 'valid' => 0, 'use_field' => 1])->persist();
+        MailFieldsFactory::make(['mail_content_id' => 1, 'field_name' => 'name_1', 'valid' => 1, 'use_field' => 1])->persist();
         ContentFactory::make(['id' => 1, 'plugin' => 'BcMail', 'type' => 'MailContent', 'entity_id' => 1, 'url' => '/contact/', 'site_id' => 1, 'lft' => 1, 'rght' => 2])->persist();
         MailContentFactory::make([
             'id' => 1,
@@ -170,10 +170,15 @@ public function testSubmit()
             'sender_1' => 't@gm.com'
         ])->persist();
 
+        // 回帰テスト: バリデーションエラー時に 500 にならず確認画面を再表示する
         $this->session(['BcMail' => ['valid' => true]]);
-        $this->post('/contact/submit/', ['sex' => 1]);
-        $this->assertResponseCode(302);
-        $this->assertRedirect('/contact/thanks');
+        $this->post('/contact/submit/', ['sex' => 1, 'name_1' => '']);
+        $this->assertResponseCode(200);
+        $vars = $this->_controller->viewBuilder()->getVars();
+        $this->assertNotNull($vars['mailContent']);
+        $this->assertNotNull($vars['mailFields']);
+        $this->assertNotNull($vars['mailMessage']);
+        $this->assertArrayHasKey('name_1', $vars['mailMessage']->getErrors());
     }
 
     /**