A VIN storage electronic control unit stores a vehicle identification number (VIN). A standby RAM that holds data constantly with an electric power supplied by a battery stores failure diagnosis related information and a rewriting history flag. When the VIN storage electronic control unit rewrites the VIN upon receiving a request signal for rewriting the VIN, the standby RAM updates the rewriting history flag so as to switch into a set status indicating the rewriting is made. When receiving a request signal for eliminating the failure diagnosis related information, the failure diagnosis related information stored in the standby RAM is reset and the rewriting history flag is switched into a reset status. In addition, while the rewriting history flag is in the set status, a malfunction indicator lamp is turned on.