To monitor a plurality of automobiles to prevent the burglar and mischief without inconveniences on user and management sides.

A portable driver transmitting means 3 outputs an ON/OFF instruction signal of guard instruction to a transmitting and receiving means 2 loaded on an automobile 1. The transmitting and receiving means 2 is set to guard state on receipt of the ON signal of guard instruction to output the signal of ID code of the automobile to a receiving means 4 arranged out of the automobile, and the receiving means 4 stores the time data of the start of guard state together with the ID code. The transmitting and receiving means 2 outputs an output signal for locking the chain 9 of a parking garage gate on the basis of the detection of a detecting means such as vibration sensor or door opening and closing sensor provided on the automobile 1 to a transmitting device 11, and the receiving means 4 alarms it to a manager by a buzzer or lamp. Further, the alarm signal is transmitted to an external guard security company through a communication line 51.