To discriminate failure of load current of a positive/negative power supply with higher accuracy.

An electro magnetically coupled pickup coil 30 is provided between the center tap 14 of a center tap bridge rectifying circuit 12 and a ground point 30 of the positive/negative power supplies 16, 18. If a short-circuit of transistor 24 occurs, a voltage difference (load current difference) of the positive/negative power supplies 16, 18 is generated at the ground point 20 and an unbalance current flows between the earth point 20 and the center tap 14. When the unbalance current flows, a current is induced in the pickup coil 30 and this current is then inputted to an operational input amplifier 30 and a signal is then inputted to a microcomputer 34 from the operation input amplifier 32. Therefore, when this signal is inputted, the microcomputer 34 discriminates that an unbalance current has flowed between the ground point 20 of the positive/negative power supplies 16, 18 and the center tap 14, namely that a failure is generated in the load current of the positive/negative power supplies 16, 18.