PURPOSE: To prevent such a keyhole-left alarm due to its own device from occurring at the unnecessary time of such a warning as in time of boarding.

CONSTITUTION: This device is provided with a key turning detecting sensor 12 detecting a switching operation to the specified position, for example, an automatic combustion control(ACC) position by an ignition switch. After a fact that a door at the driver's seat is in a state of being opened is detected by a driver's seat door switch 14, an ignition key is inserted into a keyhole by a handle lock switch 13, whereby no warning is emitted by an alarm device till a fact that the ignition key is switched to the specified position is detected by the key turning detecting sensor 12.