PURPOSE: To quicken the response speed and to decrease the distortion of an output power waveform by limiting the amplitude of an input voltage signal by a differential amplifier type limiter circuit, converting the limited signal into a differential current signal, driving a current drive switching circuit with this signal to obtain a voltage signal and using the voltage signal so as to drive a load drive circuit.

CONSTITUTION: An input voltage signal is inputted to a differential amplifier limiter circuit 4 via a coupling capacitor 2, a differential voltage signal output of the limiter circuit is converted into a differential current signal by a differential voltage-current drive circuit 5, the differential current output drives 1st and 2nd current drive switching circuits 6, 7, and a voltage output resulting from to the current change of the two current drive switching circuits drives a load drive circuit 9. The current drive switching circuits 6, 7 act like setting the amplitude voltage width at the output terminal and setting an average DC voltage at the output terminal. The load drive circuit assists the constant current source to enhance the drive capability, discharges the charging voltage due to the stray capacitance of the load of the like especially thereby improving the waveform distortion from an 'H' level to an 'L' level.