A first and a second semiconductor switching elements are provided in parallel between a first supply voltage and a second negative reference voltage to become conductive based on an input signal. A first and a second high breakdown voltage semiconductor switching elements are provided in serial to the first and second semiconductor switching elements and kept normally conductive. A first current source circuit supplies a first current to the first and second semiconductor switching elements. A second current source circuit is connected in parallel with the first current source to supply a second current only for a certain period of time.