through a parallel circuit consisting of a resistor r 1 and a capacitor c 1 on the primary side of the pulse transformer t two primary coils p 1 and p 2 are arranged in opposite phases to each other the collector of a conventional bipolar transistor q 2 is connected to the first primary coil p 1 while the drain of a mos type fet q 3 which functions as the second switching element is connected to the second primary coil p 2 in addition a diode d 1 which functions as a feedback circuit is connected in the reverse direction from the collector terminal of the transistor q 2 to the gate terminal of the fet q 3 while a diode d 2 which functions as a feedback circuit is connected in the reverse direction from the drain terminal of the fet q 3 to the base terminal of the transistor q 2 further a diode d 3 is connected in the forward direction between the emitter of the transistor q 2 and ground whereby the potential difference of the transistor q 2 relative to ground is raised by an amount corresponding to the forward potential difference across the diode d 3 meanwhile a control circuit 3 which delivers control signals to the pre drive circuit 2 has a signal output transistor.