Based upon the results of an ID check with an ignition knob lock device which prevents rotational operation of an ignition knob which is used when stating an engine of a vehicle, and of an ID check with a portable unit, a passive control unit transmits to the ignition knob lock device a command to release prohibition of rotational operation of the ignition knob, and performs an ID check with the ignition knob lock device before detecting an operation of pushing in the ignition knob.