PURPOSE: To prevent burglar by providing a detection signal canceling means to invalidate the output of a switching means to an alarm controlling circuit in a state to maintain an armed state when a regular unlocking signal is generated.
CONSTITUTION: An infrared-ray light receiving circuit 141 is provided to the rear of a vehicle, and it is connected to a detection signal canceling circuit 140. An output is provided to a timer 144 when a comparator 142 in the circuit 140 compares the output signal from the circuit 141 with a code signal stored in a memory circuit 143 and when they match with each other. In addition, an actuator 145 to unlock a locking device is operated to open a trunk lid 87. Then, even if the output of a short pulse width is generated from a one-shot multivibrator 146, the output of the trunk lid 87 is so invalidated that an RS flip-flop 97 remains in a state of setting without operating a one-shot vibrator 148 to change-over automatically in a state of alarm.