PURPOSE: To increase the load current by detecting an output current by the voltage between the drain and the source of a power transistor TR to eliminate a need of a sense resistance for current detection and reducing the output impedance.

CONSTITUTION: A voltage VD between the drain D and the source S of an output power TR 2 is detected by a comparator 4a of an output detecting part 3a and is divided by the on-state resistance to obtain the value of an output current i0 of the output power TR 2. Simultaneously, a gate voltage VG and a prescribed voltage value are detected and compared by a comparator 4b to confirm the operating state of the power TR 2. Output signals Sea and 845 of comparators 4a and 4b are inputted to an AND gate 5, and an output overcurrent detection signal S5 is fed back to a gate driver 1 to control inhibition/passage of the gate voltage VG. Thus, the output impedance viewed from an output terminal is reduced to increase the output current.