PURPOSE: To enhance the function of theft prevention even when a device number storage element or a printed circuit board is replaced by devising this system such that a sensor section on the printed circuit board detects the device number of an enclosure and the device number is correlated with a device number stored in the device number storage element so as to operate the automobile telephone circuit.

CONSTITUTION: A device number is given to the enclosure 1 and a printed circuit board fixed to the enclosure 1 is provided with a sensor section 2 to read the device number and a control section 3 taking correlation between the device number detected by the sensor section 2 and the device number stored in the device number storage element 5 and controlling the automobile telephone circuit 4. Thus, the theft prevention is enhanced even when the device number storage element or the printed circuit board is replaced.