diff --git a/README.md b/README.md
index 256b83f..243f541 100644
--- a/README.md
+++ b/README.md
@@ -42,81 +42,12 @@ Current images use fluentd v1 series.
 
 We recommend to use debian version for production because it uses jemalloc to mitigate memory fragmentation issue.
 
+If you want to know the detail of supported image tags, see [TAGRULE](TAGRULE.md) explanation.
+
 ### Using Kubernetes?
 
 Check [fluentd-kubernetes-daemonset](https://github.com/fluent/fluentd-kubernetes-daemonset) images.
 
-## The detail of image tag
-
-This image is based on the popular Debian images and [Alpine Linux project][1], available in
-[the alpine official image][2].
-
-### For current images
-
-#### `edge`
-
-Latest released version of Fluentd.
-
-#### `vX.Y-A`
-
-Latest version of `vX.Y` Fluentd branch.
-
-`A` will be incremented when image has major changes.
-
-When fluentd version is updated, A is reset to `1`.
-
-#### `vX.Y.Z-A.B`
-
-Concrete `vX.Y.Z` version of Fluentd. This tag is recommeded for the production environment.
-
-`A` will be incremented when image has major changes.
-`B` will be incremented when image has small changes, e.g. library update or bug fixes.
-
-When fluentd version is updated, `A.B` is reset to `1.0`.
-
-#### `debian` included tag
-
-The image based on [Debian Linux image][7].
-You may use this image when you require plugins which cannot be installed on Alpine (like `fluent-plugin-systemd`).
-
-#### `armhf` included tag
-
-The `armhf` images use ARM base images for use on devices such as Raspberry Pis.
-
-Furthermore, the base images enable support for cross-platform builds using the cross-build tools from [resin.io](https://docs.resin.io/reference/base-images/resin-base-images/#resin-xbuild-qemu).
-
-In order to build these images natively on ARM devices, the `CROSS_BUILD_START` and `CROSS_BUILD_END` Docker build arguments must be set to the shell no-op (`:`), for example:
-```bash
-docker build --build-arg CROSS_BUILD_START=":" --build-arg CROSS_BUILD_END=":" -t fluent/fluentd:v1.3-onbuild-1 v1.3/armhf/alpine-onbuild
-```
-(assuming the command is run from the root of this repository).
-
-### For older images
-
-These images/tags are kept for backward compatibility. No update anymore and don't use for new deployment. Use "current images" instead.
-
-#### `stable`, `latest`
-
-These tags are obsolete, already removed to avoid confusing.
-Use `edge`, `vX.Y-A` or `vX.Y.Z-A.B` images instead.
-
-#### `vX.Y`
-
-Latest version of `vX.Y` Fluentd branch.
-
-#### `vX.Y.Z`
-
-Concrete `vX.Y.Z` version of Fluentd.
-
-#### `onbuild` included tag
-
-`onbuild` images are deprecated. Use non-`onbuild ` images instead to build your image.
-New images, v1.5 or later, don't provide `onbuild` version.
-
-#### `debian` included tag, `armhf` included tag
-
-Same as current images.
-
 ## How to use this image
 
 To create endpoint that collects logs on your host just run:
diff --git a/TAGRULE.md b/TAGRULE.md
new file mode 100644
index 0000000..ca44446
--- /dev/null
+++ b/TAGRULE.md
@@ -0,0 +1,70 @@
+# The detail of image tag
+
+This image is based on the popular Debian images and [Alpine Linux project][1], available in
+[the alpine official image][2].
+
+## For current images
+
+### `edge`
+
+Latest released version of Fluentd.
+
+### `vX.Y-A`
+
+Latest version of `vX.Y` Fluentd branch.
+
+`A` will be incremented when image has major changes.
+
+When fluentd version is updated, A is reset to `1`.
+
+### `vX.Y.Z-A.B`
+
+Concrete `vX.Y.Z` version of Fluentd. This tag is recommeded for the production environment.
+
+`A` will be incremented when image has major changes.
+`B` will be incremented when image has small changes, e.g. library update or bug fixes.
+
+When fluentd version is updated, `A.B` is reset to `1.0`.
+
+### `debian` included tag
+
+The image based on [Debian Linux image][7].
+You may use this image when you require plugins which cannot be installed on Alpine (like `fluent-plugin-systemd`).
+
+### `armhf` included tag
+
+The `armhf` images use ARM base images for use on devices such as Raspberry Pis.
+
+Furthermore, the base images enable support for cross-platform builds using the cross-build tools from [resin.io](https://docs.resin.io/reference/base-images/resin-base-images/#resin-xbuild-qemu).
+
+In order to build these images natively on ARM devices, the `CROSS_BUILD_START` and `CROSS_BUILD_END` Docker build arguments must be set to the shell no-op (`:`), for example:
+```bash
+docker build --build-arg CROSS_BUILD_START=":" --build-arg CROSS_BUILD_END=":" -t fluent/fluentd:v1.3-onbuild-1 v1.3/armhf/alpine-onbuild
+```
+(assuming the command is run from the root of this repository).
+
+## For older images
+
+These images/tags are kept for backward compatibility. No update anymore and don't use for new deployment. Use "current images" instead.
+
+#### `stable`, `latest`
+
+These tags are obsolete, already removed to avoid confusing.
+Use `edge`, `vX.Y-A` or `vX.Y.Z-A.B` images instead.
+
+### `vX.Y`
+
+Latest version of `vX.Y` Fluentd branch.
+
+### `vX.Y.Z`
+
+Concrete `vX.Y.Z` version of Fluentd.
+
+### `onbuild` included tag
+
+`onbuild` images are deprecated. Use non-`onbuild ` images instead to build your image.
+New images, v1.5 or later, don't provide `onbuild` version.
+
+### `debian` included tag, `armhf` included tag
+
+Same as current images.