PURPOSE: To prevent the circuit parts of a CMOS system on a printed circuit board from being destroyed by turning off a power source supplied to the circuit parts of the CMOS system just after an excess current such as latch-up, etc., flows.

CONSTITUTION: A feeding layer 12a for CMOS parts and a feeding layer 12b for bipolar parts execute feeding to CMOS system circuit parts 13a-13c and bipolar system circuit parts 14a-14c on a printed circuit board 11 separately from a power supply part 17. A current value monitor circuit 15 monitors the current flowing from the feeding layer 12a for CMOS parts by a sensor 15a. When the excess current is detected, according to an instruction from the current value monitor circuit 15, a power source turn-off circuit 16 turns off the power source of the feeding layer 12a for CMOS parts.