PURPOSE: To cause both forward and reverse base currents to flow surely through a simple circuit constitution by connecting four sets of semiconductor switching elements with a bridge circuit and by simultaneously ON-OFF controlling respective semiconductor switching elements arranged on the opposite sides of said bridge circuit.

CONSTITUTION: When a control signal is applied to a control terminal 19 to turn ON semiconductor switching elements 3 and in a state where a power source is connected with a terminal 12 in a bridge circuit bridge-connecting four sets of semiconductor switching elements 3, 6, 7, 10, a current limited by a resistance 4 flow as a forward current between the base and emitter of a power transistor 1 to apply current to said power transistor 1. Also, when the control signal of said control terminal 19 is interrupted and a control signal is applied to a control terminal 20 to turn ON semiconductor switching elements 7 and 10, a current is hindered from flowing to the power transistor 1. Thus, it is possible to achieve the miniaturization of an apparatus and to stop the power application to said power transistor surely.