diff --git a/.github/workflows/verify-on-macos.yml b/.github/workflows/verify-on-macos.yml
index 14653ca..469120b 100644
--- a/.github/workflows/verify-on-macos.yml
+++ b/.github/workflows/verify-on-macos.yml
@@ -13,7 +13,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
     - name: print created files
       run: ls -l ~/.ssh
     - name: git clone through SSH
@@ -28,7 +28,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
         name: ssh_key_name # optional
         config: | # optional
           Host github
diff --git a/.github/workflows/verify-on-ubuntu.yml b/.github/workflows/verify-on-ubuntu.yml
index f50b4cd..e6548e1 100644
--- a/.github/workflows/verify-on-ubuntu.yml
+++ b/.github/workflows/verify-on-ubuntu.yml
@@ -13,7 +13,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
     - name: print created files
       run: ls -l ~/.ssh
     - name: git clone through SSH
@@ -28,7 +28,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
         name: ssh_key_name # optional
         config: | # optional
           Host github
diff --git a/.github/workflows/verify-on-ubuntu1604.yml b/.github/workflows/verify-on-ubuntu1604.yml
index 7024e65..b3cce08 100644
--- a/.github/workflows/verify-on-ubuntu1604.yml
+++ b/.github/workflows/verify-on-ubuntu1604.yml
@@ -13,7 +13,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
     - name: print created files
       run: ls -l ~/.ssh
     - name: git clone through SSH
@@ -28,7 +28,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
         name: ssh_key_name # optional
         config: | # optional
           Host github
diff --git a/.github/workflows/verify-on-windows.yml b/.github/workflows/verify-on-windows.yml
index a2332dd..003466f 100644
--- a/.github/workflows/verify-on-windows.yml
+++ b/.github/workflows/verify-on-windows.yml
@@ -13,7 +13,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
     - name: print created files
       run: ls ~/.ssh
     - name: git clone through SSH
@@ -28,7 +28,7 @@ jobs:
       uses: ./.
       with:
         key: ${{ secrets.SSH_KEY }}
-        known-hosts: ${{ secrets.KNOWN_HOSTS }} # optional
+        known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
         name: ssh_key_name # optional
         config: | # optional
           Host github
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8746d25..55bebe3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 
 * rename `private-key` to `key`
+* rename `known-hosts` to `known_hosts`
 
 ## [1.6.4] - 2020-01-27
 
diff --git a/README.md b/README.md
index d3e9bc7..ac298dc 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@ steps:
   with:
     key: ${{ secrets.SSH_KEY }}
     name: id_rsa # optional
-    known-hosts: ${{ secrets.KNOWN_HOSTS }} # known_hosts; optional
+    known_hosts: ${{ secrets.KNOWN_HOSTS }} # optional
     config: ${{ secrets.CONFIG }} # ssh_config; optional
 - name: rsync over ssh
   run: rsync ./foo/ user@remote:bar/
@@ -42,7 +42,7 @@ See [Workflow syntax for GitHub Actions](https://help.github.com/en/articles/wor
 If you want to install multiple keys, call this action multiple times.
 It is useful for port forwarding.
 
-**NOTE:**  When this action is called multiple times, **the contents of `known-hosts` and `config` will be appended**. `key` must be saved as different name, by using `name` option.
+**NOTE:**  When this action is called multiple times, **the contents of `known_hosts` and `config` will be appended**. `key` must be saved as different name, by using `name` option.
 
 ```yaml
 runs-on: ubuntu-latest
@@ -52,7 +52,7 @@ steps:
   with:
     key: ${{ secrets.SSH_KEY_OF_BASTION }}
     name: id_rsa-bastion
-    known-hosts: ${{ secrets.KNOWN_HOSTS_OF_BASTION }}
+    known_hosts: ${{ secrets.KNOWN_HOSTS_OF_BASTION }}
     config: |
       Host bastion
         HostName xxx.xxx.xxx.xxx
@@ -63,7 +63,7 @@ steps:
   with:
     key: ${{ secrets.SSH_KEY_OF_TARGET }}
     name: id_rsa-target
-    known-hosts: ${{ secrets.KNOWN_HOSTS_OF_TARGET }} # will be appended!
+    known_hosts: ${{ secrets.KNOWN_HOSTS_OF_TARGET }} # will be appended!
     config: |                                         # will be appended!
       Host target
         HostName yyy.yyy.yyy.yyy
@@ -84,9 +84,9 @@ Check belows:
     * OPENSSH format (key begins with `-----BEGIN OPENSSH PRIVATE KEY-----`) may not work.
     * Use PEM format (begins with `-----BEGIN RSA PRIVATE KEY-----`).
 * `Host key verification failed.`:
-    * Set `known-hosts` option or use `ssh -o StrictHostKeyChecking=no`.
+    * Set `known_hosts` option or use `ssh -o StrictHostKeyChecking=no`.
     * The former is **HIGHLY** recommended for security reason.
-    * I'm planning to make `known-hosts` required in v2.
+    * I'm planning to make `known_hosts` required in v2.
 
 ### How do I use encrypted SSH key?
 
@@ -104,7 +104,7 @@ I recommend **rsync via bastion**.
 It has some advantages over other methods:
 
 * "Rsync via bastion" doesn't require to update workflow files and `secrets` even if it is necessary to transfer files to multiple servers.
-    * Other methods require to update `known-hosts` if servers have changed.
+    * Other methods require to update `known_hosts` if servers have changed.
 * Rsync:
     * is fastest of all.
     * does **NOT** break files even if disconnected during transferring.
diff --git a/action.yml b/action.yml
index 9974c8b..aef5b4e 100644
--- a/action.yml
+++ b/action.yml
@@ -13,7 +13,7 @@ inputs:
     description: "SSH key file name (default: id_rsa)"
     required: false
     default: "id_rsa"
-  known-hosts:
+  known_hosts:
     description: "public keys of SSH servers"
     required: false
     default: ""
diff --git a/lib/main.js b/lib/main.js
index ede1edf..b97cccb 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -28,7 +28,7 @@ function main() {
             },
             {
                 name: "known_hosts",
-                contents: prependLf(core.getInput("known-hosts")),
+                contents: prependLf(core.getInput("known_hosts")),
                 options: {
                     mode: 0o644,
                     flag: "a",
diff --git a/src/main.ts b/src/main.ts
index 62a5520..b3aa60c 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -30,7 +30,7 @@ function main(): void
 			},
 			{
 				name: "known_hosts",
-				contents: prependLf(core.getInput("known-hosts")),
+				contents: prependLf(core.getInput("known_hosts")),
 				options: {
 					mode: 0o644,
 					flag: "a",