PURPOSE: To suppress overcurrent, by performing control such that the switching period of a noncontact switching element is lengthened based on a comparison result between a detected voltage of a load current detection circuit and a reference voltage and performing regulation such that the impedance of an impedance circuit increases.

CONSTITUTION: When overcurrent flows through a brushless motor 1, level of voltage Vd detected through a load current detecting circuit 17 increases. When a difference between the detected voltage Vd and a reference voltage Vs fed from a current setting circuit 13 exceeds over a preset limit level, a control circuit 3 performs control such that the output period of ON command signals S1, S2 from transistors 11, 12 is lengthened so as to increase the impedance of an impedance circuit 4. Consequently, output voltage Vout from the impedance circuit 4 drops to decrease load current flowing through the impedance 4.