PURPOSE: To simplify the base drive circuit or its peripheral circuit and to reduce the cost by connecting a power MOSFET in cascade to the pre-stage of a power bipolar transistor(TR).

CONSTITUTION: A drain D and a source S of a pre-stage N-channel power MOSFET 1 are connected respectively to a collector C and a base B of a post- stage NPN power TR 2. With a positive bias applied to a gate terminal of the MOSFET 1 with respect to an emitter terminal 4, the drain-source of the pre-stage power MOSFET 1 is conductive. Then the base of the post-stage bipolar TR 2 is biased forward and the collector-emitter is conductive. The switching circuit is activated by having only to apply a voltage to the gate 3 through the cascade connection of the power MOSFET 1 and the power bipolar TR 2 in this way. Thus, the base drive circuit or its peripheral circuit is simplified and the cost is reduced.