PURPOSE: To compensate the intense distortion waveform of voltage with high speed response by integrating the detected value of a source voltage to a CR waveform circuit, comparing the output from the CR waveform circuit and the output from a saw tooth wave generating circuit and applying the result thereof to a firing circuit.

CONSTITUTION: The integrated result by an integrating means 6 is fed to a circuit 11 for taking in the integrated output. An electronic switch 7, on receiving the output signal from said circuit, turns on to take said signal in a C.R waveform circuit 8. After the signal is taken into the C.R waveform circuit, the means 6 is reset by the signal of an integration resetting circuit. The operation of integrating the detection voltage from a source voltage detecting circuit 1 is again repeated after the annihilation of the reset signal and the distortion waveform is averaged by every 1/2 cycle. The control for compensation with 1/2 cycle response is accomplished by the succeeding stage of the C.R waveform circuit 8 and comparator 4. The compensation of the integrated signal with high accuracy is made possible over the entire region of a phase adjustment.