diff --git a/ChangeLog b/ChangeLog
index 4b2061a..c8bd20d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2017-10-06  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* src/configure: Allow not specifying VIDPID.
+
+	* src/main.c [GNU_LINUX_EMULATION] (main): Handle "--vidpid"
+	option to assign vendor ID and product ID of USB.
+
+	* src/usb_desc.c [GNU_LINUX_EMULATION] (device_desc): Export.
+
+	* GNUK_USB_DEVICE_ID (0000:0000): New.
+
 2017-10-05  NIIBE Yutaka  <gniibe@fsij.org>
 
 	* src/stack-def.h (SIZE_1, SIZE_3): Tweak the size.
diff --git a/GNUK_USB_DEVICE_ID b/GNUK_USB_DEVICE_ID
index b62527f..003f4ee 100644
--- a/GNUK_USB_DEVICE_ID
+++ b/GNUK_USB_DEVICE_ID
@@ -1,4 +1,5 @@
 # VID:PID	bcdDev	Product_STRING	Vendor_STRING
+0000:0000	0200	Gnuk Emulation	Free Software Initiative of Japan
 234b:0000	0200	Gnuk Token	Free Software Initiative of Japan
 20a0:4211	0200	Nitrokey Start	Nitrokey
 ##########<TAB>	##<TAB>	##########<TAB>	#################
diff --git a/src/configure b/src/configure
index d51ff7d..9e04f94 100755
--- a/src/configure
+++ b/src/configure
@@ -162,11 +162,6 @@ EOF
   exit 0
 fi
 
-if test "$vidpid" = "none"; then
-  echo "Please specify Vendor ID and Product ID by --vidpid option." >&2
-  exit 1
-fi
-
 BOARD_HEADER_FILE=board-$(echo $target | tr '_[:upper:]' '-[:lower:]').h
 echo "Header file is: $BOARD_HEADER_FILE"
 ln -sf "../chopstx/board/$BOARD_HEADER_FILE" board.h
@@ -227,6 +222,17 @@ else
   libs=""
 fi
 
+if test "$emulation" = "yes"; then
+  if test "$vidpid" = "none"; then
+     vidpid=0000:0000
+  fi
+else
+  if test "$vidpid" = "none"; then
+    echo "Please specify Vendor ID and Product ID by --vidpid option." >&2
+  exit 1
+  fi
+fi
+
 # --enable-debug option
 if test "$debug" = "yes"; then
   DEBUG_MAKE_OPTION="ENABLE_DEBUG=1"
diff --git a/src/main.c b/src/main.c
index aa54935..1cdaee1 100644
--- a/src/main.c
+++ b/src/main.c
@@ -233,12 +233,34 @@ main (int argc, const char *argv[])
 #ifdef GNU_LINUX_EMULATION
 #define FLASH_IMAGE_NAME ".gnuk-flash-image"
 
-  if (argc >= 3 || (argc == 2 && !strcmp (argv[1], "--help")))
+  if (argc >= 4 || (argc == 2 && !strcmp (argv[1], "--help")))
     {
-      fprintf (stdout, "Usage: %s [flash-image-file]", argv[0]);
+      fprintf (stdout, "Usage: %s [--vidpid=Vxxx:Pxxx] [flash-image-file]",
+	       argv[0]);
       exit (0);
     }
 
+  if (argc >= 2 && !strncmp (argv[1], "--vidpid=", 9))
+    {
+      extern uint8_t device_desc[];
+      uint32_t id;
+      char *p;
+
+      id = (uint32_t)strtol (&argv[1][9], &p, 16);
+      device_desc[8] = (id & 0xff);
+      device_desc[9] = (id >> 8);
+
+      if (p && p[0] == ':')
+	{
+	  id = (uint32_t)strtol (&p[1], NULL, 16);
+	  device_desc[10] = (id & 0xff);
+	  device_desc[11] = (id >> 8);
+	}
+
+      argc--;
+      argv++;
+    }
+
   if (argc == 1)
     {
       char *p = getenv ("HOME");
diff --git a/src/usb_desc.c b/src/usb_desc.c
index a5a1594..8031088 100644
--- a/src/usb_desc.c
+++ b/src/usb_desc.c
@@ -59,7 +59,10 @@ static const uint8_t hid_report_desc[] = {
 #define USB_CCID_DATA_SIZE 64
 
 /* USB Standard Device Descriptor */
-static const uint8_t device_desc[] = {
+#if !defined(GNU_LINUX_EMULATION)
+static const
+#endif
+uint8_t device_desc[] = {
   18,   /* bLength */
   DEVICE_DESCRIPTOR,     /* bDescriptorType */
   0x10, 0x01,   /* bcdUSB = 1.1 */