To carry out an alarm system release even the battery capacity of a transmitter for a keyless remote control entry is dropped.

A battery monitor circuit 91 for detecting the capacity of a battery 51 is installed in a transmitter 39. A battery capacity information is written in the memory of a transponder chip and this battery capacity information is sent to an imobilizer control unit as well as the key discrimination information of the transponder chip. A theft prevention control unit releases the output of a theft warning order by the comparison of a keyless discrimination number from the transmitter 39 except at the lack time of the battery capacity and releases the output of a theft warning order by the comparison of a key discrimination information instead of the comparison of the keyless discrimination number on only the lack time of the battery capacity and that the unlock switch of a door key cylinder is turned on.