PURPOSE: To eliminate a danger of wrong explosion even in the case of generating a connector short with a high accuracy safely detecting a resistance value of a squib, in an air bag ECU.

CONSTITUTION: A transistor TR1 and a resistor R1 are connected in series between one end of a resistance measuring power supply and a squib SQ, and a transistor TR2 and a resistor R2 are connected in series between the squib and the other end of the power supply, to control the transistors TR1, TR2 instantaneously turned on by a CPU only while a resistance value of the squib is measured. In the case of a connector short, a current is limited by the resistors R1, R2.