diff --git a/common.mk b/common.mk
index 86518f03..de22f2c8 100644
--- a/common.mk
+++ b/common.mk
@@ -3,6 +3,7 @@ SRC +=	$(COMMON_DIR)/host.c \
 	$(COMMON_DIR)/keyboard.c \
 	$(COMMON_DIR)/action.c \
 	$(COMMON_DIR)/action_macro.c \
+	$(COMMON_DIR)/layer_stack.c \
 	$(COMMON_DIR)/keymap.c \
 	$(COMMON_DIR)/command.c \
 	$(COMMON_DIR)/timer.c \
diff --git a/common/action.c b/common/action.c
index 38c5933e..9a8d7559 100644
--- a/common/action.c
+++ b/common/action.c
@@ -24,6 +24,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "util.h"
 #include "debug.h"
 #include "action.h"
+#include "layer_stack.h"
 
 
 /* default layer indicates base layer */
@@ -163,85 +164,6 @@ static void oneshot_toggle(void)
 }
 
 
-/*
- * Layer stack
- */
-#define LAYER_STACK_SIZE 8
-typedef struct {
-    uint8_t layer:4;
-    uint8_t next:3;
-    bool    used;
-} layer_item_t;
-
-static uint8_t top_layer = 0;
-// [0] is sentinel and not used. [0] is null item.
-static layer_item_t layer_stack[LAYER_STACK_SIZE] = {};
-
-static bool layer_push(uint8_t layer)
-{
-    for (uint8_t i = 1; i < LAYER_STACK_SIZE; i++) {
-        if (!layer_stack[i].used) {
-            layer_stack[i] = (layer_item_t){ .layer = layer,
-                                              .next = top_layer,
-                                              .used = true };
-            top_layer = i;
-            return true;
-        }
-    }
-    return false;
-}
-static bool layer_pop(void)
-{
-    if (layer_stack[top_layer].used) {
-        uint8_t popped = top_layer;
-        top_layer = layer_stack[popped].next;
-        layer_stack[popped] = (layer_item_t){};
-        return true;
-    }
-    return false;
-}
-static bool layer_remove(uint8_t layer)
-{
-    if (layer_stack[top_layer].used && layer_stack[top_layer].layer == layer) {
-        layer_pop();
-        debug("layer_remove: top_layer\n");
-        return true;
-    }
-
-    for (uint8_t i = top_layer; layer_stack[i].used; i = layer_stack[i].next) {
-        debug("layer_remove: ["); debug_dec(i); debug("]");
-        debug_dec(layer_stack[i].layer); debug("\n");
-        uint8_t removed = layer_stack[i].next;
-        if (layer_stack[removed].used && layer_stack[removed].layer == layer) {
-            layer_stack[i].next = layer_stack[removed].next;
-            layer_stack[removed] = (layer_item_t){};
-            debug("layer_remove: removed.\n");
-            return true;
-        }
-    }
-    return false;
-}
-static bool layer_remove_then_push(uint8_t layer)
-{
-    layer_remove(layer);
-    return layer_push(layer);
-}
-static bool layer_remove_or_push(uint8_t layer)
-{
-    return (layer_remove(layer)) || layer_push(layer);
-}
-static void debug_layer_stack(void)
-{
-    debug("layer_stack: ");
-    layer_item_t item = layer_stack[top_layer];
-    while (item.used) {
-        debug_dec(item.layer);
-        debug("["); debug_dec(item.next); debug("]");
-        item = layer_stack[item.next];
-    }
-    debug("\n");
-}
-
 
 void action_exec(keyevent_t event)
 {
@@ -292,14 +214,9 @@ static action_t get_action(key_t key)
     action.code = ACTION_NO;
 
     /* layer stack */
-    for (layer_item_t i = layer_stack[top_layer]; i.used; i = layer_stack[i.next]) {
-        action = action_for_key(i.layer, key);
-        if (action.code != ACTION_TRANSPARENT) {
-            debug_layer_stack();
-            debug("layer_stack: used. "); debug_dec(i.layer); debug("\n");
-            return action;
-        }
-        debug("layer_stack: through. "); debug_dec(i.layer); debug("\n");
+    action = layer_stack_get_action(key);
+    if (action.code != ACTION_TRANSPARENT) {
+        return action;
     }
 
     /* current layer: 0 means default layer */
@@ -618,41 +535,41 @@ static void process_action(keyrecord_t *record)
             switch (action.layer.code) {
                 case LAYER_MOMENTARY:  /* momentary */
                     if (event.pressed) {
-                        layer_remove_then_push(action.layer.val);
-                        debug_layer_stack();
+                        layer_stack_remove_then_push(action.layer.val);
+                        layer_stack_debug();
                     } else {
-                        layer_remove(action.layer.val);
-                        debug_layer_stack();
+                        layer_stack_remove(action.layer.val);
+                        layer_stack_debug();
                     }
                     break;
                 case LAYER_ON_PRESS:
                     if (event.pressed) {
-                        layer_remove_or_push(action.layer.val);
-                        debug_layer_stack();
+                        layer_stack_remove_or_push(action.layer.val);
+                        layer_stack_debug();
                     }
                     break;
                 case LAYER_ON_RELEASE:
                     if (!event.pressed) {
-                        layer_remove_or_push(action.layer.val);
-                        debug_layer_stack();
+                        layer_stack_remove_or_push(action.layer.val);
+                        layer_stack_debug();
                     }
                     break;
                 case LAYER_ON_BOTH:
-                    layer_remove_or_push(action.layer.val);
-                    debug_layer_stack();
+                    layer_stack_remove_or_push(action.layer.val);
+                    layer_stack_debug();
                     break;
                 case LAYER_TAP_TOGGLE:  /* switch on hold and toggle on several taps */
                     if (event.pressed) {
                         if (tap_count < TAPPING_TOGGLE) {
                             debug("LAYER_STACK: tap toggle(press).\n");
-                            layer_remove_or_push(action.layer.val);
-                            debug_layer_stack();
+                            layer_stack_remove_or_push(action.layer.val);
+                            layer_stack_debug();
                         }
                     } else {
                         if (tap_count <= TAPPING_TOGGLE) {
                             debug("LAYER_STACK: tap toggle(release).\n");
-                            layer_remove_or_push(action.layer.val);
-                            debug_layer_stack();
+                            layer_stack_remove_or_push(action.layer.val);
+                            layer_stack_debug();
                         }
                     }
                     break;
@@ -664,8 +581,8 @@ static void process_action(keyrecord_t *record)
                             register_code(action.layer.code);
                         } else {
                             debug("LAYER_STACK: No tap: layer_stack(on press)\n");
-                            layer_remove_or_push(action.layer.val);
-                            debug_layer_stack();
+                            layer_stack_remove_or_push(action.layer.val);
+                            layer_stack_debug();
                         }
                     } else {
                         if (IS_TAPPING_KEY(event.key) && tap_count > 0) {
@@ -673,8 +590,8 @@ static void process_action(keyrecord_t *record)
                             unregister_code(action.layer.code);
                         } else {
                             debug("LAYER_STACK: No tap: layer_stack(on release)\n");
-                            layer_remove_or_push(action.layer.val);
-                            debug_layer_stack();
+                            layer_stack_remove_or_push(action.layer.val);
+                            layer_stack_debug();
                         }
                     }
                     break;
diff --git a/common/layer_stack.c b/common/layer_stack.c
new file mode 100644
index 00000000..07c84870
--- /dev/null
+++ b/common/layer_stack.c
@@ -0,0 +1,100 @@
+#include <stdint.h>
+#include "keyboard.h"
+#include "layer_stack.h"
+#include "debug.h"
+
+
+static uint8_t top_layer = 0;
+
+/* [0] always works as sentinel and not used for store.*/
+static layer_item_t layer_stack[LAYER_STACK_SIZE] = {};
+
+bool layer_stack_push(uint8_t layer)
+{
+    for (uint8_t i = 1; i < LAYER_STACK_SIZE; i++) {
+        if (!layer_stack[i].used) {
+            layer_stack[i] = (layer_item_t){ .layer = layer,
+                                              .next = top_layer,
+                                              .used = true };
+            top_layer = i;
+            return true;
+        }
+    }
+    return false;
+}
+
+bool layer_stack_pop(void)
+{
+    if (layer_stack[top_layer].used) {
+        uint8_t popped = top_layer;
+        top_layer = layer_stack[popped].next;
+        layer_stack[popped] = (layer_item_t){};
+        return true;
+    }
+    return false;
+}
+
+bool layer_stack_remove(uint8_t layer)
+{
+    if (layer_stack[top_layer].used && layer_stack[top_layer].layer == layer) {
+        layer_stack_pop();
+        debug("layer_stack_remove: top_layer\n");
+        return true;
+    }
+
+    for (uint8_t i = top_layer; layer_stack[i].used; i = layer_stack[i].next) {
+        debug("layer_stack_remove: ["); debug_dec(i); debug("]");
+        debug_dec(layer_stack[i].layer); debug("\n");
+        uint8_t removed = layer_stack[i].next;
+        if (layer_stack[removed].used && layer_stack[removed].layer == layer) {
+            layer_stack[i].next = layer_stack[removed].next;
+            layer_stack[removed] = (layer_item_t){};
+            debug("layer_stack_remove: removed.\n");
+            return true;
+        }
+    }
+    return false;
+}
+
+bool layer_stack_remove_then_push(uint8_t layer)
+{
+    layer_stack_remove(layer);
+    return layer_stack_push(layer);
+}
+
+bool layer_stack_remove_or_push(uint8_t layer)
+{
+    return (layer_stack_remove(layer)) || layer_stack_push(layer);
+}
+
+void layer_stack_debug(void)
+{
+    debug("layer_stack: ");
+    layer_item_t item = layer_stack[top_layer];
+    while (item.used) {
+        debug_dec(item.layer);
+        debug("["); debug_dec(item.next); debug("]");
+        item = layer_stack[item.next];
+    }
+    debug("\n");
+}
+
+
+
+action_t layer_stack_get_action(key_t key)
+{
+    action_t action;
+    action.code = ACTION_TRANSPARENT;
+
+    /* layer stack */
+    for (layer_item_t i = layer_stack[top_layer]; i.used; i = layer_stack[i.next]) {
+        action = action_for_key(i.layer, key);
+        if (action.code != ACTION_TRANSPARENT) {
+            layer_stack_debug();
+            debug("layer_stack: used. "); debug_dec(i.layer); debug("\n");
+            return action;
+        }
+        debug("layer_stack: through. "); debug_dec(i.layer); debug("\n");
+    }
+    return action;
+}
diff --git a/common/layer_stack.h b/common/layer_stack.h
new file mode 100644
index 00000000..c88eaffc
--- /dev/null
+++ b/common/layer_stack.h
@@ -0,0 +1,44 @@
+/*
+Copyright 2013 Jun Wako <wakojun@gmail.com>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef LAYER_STACK_H
+#define LAYER_STACK_H
+
+#include <stdint.h>
+#include "action.h"
+
+
+/*
+ * Layer stack
+ */
+#define LAYER_STACK_SIZE 8
+typedef struct {
+    uint8_t layer:4;
+    uint8_t next:3;
+    bool    used;
+} layer_item_t;
+
+
+bool layer_stack_push(uint8_t layer);
+bool layer_stack_pop(void);
+bool layer_stack_remove(uint8_t layer);
+bool layer_stack_remove_then_push(uint8_t layer);
+bool layer_stack_remove_or_push(uint8_t layer);
+void layer_stack_debug(void);
+action_t layer_stack_get_action(key_t key);
+
+#endif
+