diff --git a/.github/workflows/verify-on-container-alpine.yml b/.github/workflows/verify-on-container-alpine.yml
index e716f3b..c266aa9 100644
--- a/.github/workflows/verify-on-container-alpine.yml
+++ b/.github/workflows/verify-on-container-alpine.yml
@@ -330,3 +330,5 @@ jobs:
         known_hosts: unnecessary
     - name: print created files
       run: ls -l /root/.ssh
+    - name: git clone through SSH # can clone because key of "github.com" always set to "known_hosts"
+      run: git clone git@github.com:shimataro/ssh-key-action.git tmp
diff --git a/.github/workflows/verify-on-container-centos.yml b/.github/workflows/verify-on-container-centos.yml
index 8318e4a..667dc93 100644
--- a/.github/workflows/verify-on-container-centos.yml
+++ b/.github/workflows/verify-on-container-centos.yml
@@ -320,3 +320,5 @@ jobs:
         known_hosts: unnecessary
     - name: print created files
       run: ls -l /root/.ssh
+    - name: git clone through SSH # can clone because key of "github.com" always set to "known_hosts"
+      run: git clone git@github.com:shimataro/ssh-key-action.git tmp
diff --git a/.github/workflows/verify-on-container-ubuntu.yml b/.github/workflows/verify-on-container-ubuntu.yml
index 1abf004..4e41b6e 100644
--- a/.github/workflows/verify-on-container-ubuntu.yml
+++ b/.github/workflows/verify-on-container-ubuntu.yml
@@ -350,3 +350,5 @@ jobs:
         known_hosts: unnecessary
     - name: print created files
       run: ls -l /root/.ssh
+    - name: git clone through SSH # can clone because key of "github.com" always set to "known_hosts"
+      run: git clone git@github.com:shimataro/ssh-key-action.git tmp
diff --git a/.github/workflows/verify-on-macos.yml b/.github/workflows/verify-on-macos.yml
index e1b7e82..b631750 100644
--- a/.github/workflows/verify-on-macos.yml
+++ b/.github/workflows/verify-on-macos.yml
@@ -278,3 +278,5 @@ jobs:
         known_hosts: unnecessary
     - name: print created files
       run: ls -l ~/.ssh
+    - name: git clone through SSH # can clone because key of "github.com" always set to "known_hosts"
+      run: git clone git@github.com:shimataro/ssh-key-action.git tmp
diff --git a/.github/workflows/verify-on-ubuntu.yml b/.github/workflows/verify-on-ubuntu.yml
index f31c00d..1d0f354 100644
--- a/.github/workflows/verify-on-ubuntu.yml
+++ b/.github/workflows/verify-on-ubuntu.yml
@@ -268,3 +268,5 @@ jobs:
         known_hosts: unnecessary
     - name: print created files
       run: ls -l ~/.ssh
+    - name: git clone through SSH # can clone because key of "github.com" always set to "known_hosts"
+      run: git clone git@github.com:shimataro/ssh-key-action.git tmp
diff --git a/.github/workflows/verify-on-windows.yml b/.github/workflows/verify-on-windows.yml
index 5dc222a..60c9f7e 100644
--- a/.github/workflows/verify-on-windows.yml
+++ b/.github/workflows/verify-on-windows.yml
@@ -267,3 +267,5 @@ jobs:
         known_hosts: unnecessary
     - name: print created files
       run: ls -l ~/.ssh
+    - name: git clone through SSH # can clone because key of "github.com" always set to "known_hosts"
+      run: git clone git@github.com:shimataro/ssh-key-action.git tmp