PURPOSE: To operate an overcurrent limitation at a definite electric-power point by a method wherein an overcurrent-limiting reference voltage value is changed over when the nominal voltage of the system of an AC input is changed from a 100-V system to a 200-V system.

CONSTITUTION: Whether the distribution system of an AC input 01 is a 100-V system or a 200-V system is discriminated by an input-voltage detection circuit 10. Then, the reference voltage of an overcurrent-limiting amplifier 3 is changed over, via a reference-voltage changeover circuit 11, by the detection output of the input-voltage detection circuit 10. That is to say, when 200V AC is input, the reference-voltage generation circuit 11 generates a reference voltage which is half of 100V AC, which has been input, by the detection output of the input- voltage detection circuit 10, and it gives the reference voltage to the overcurrent- detection amplifier 3. Thereby, even when an input voltage is changed over from a 100V-system to a 200-Vsystem, an output voltage can be made nearly definite when an overcurrent is limited.