PURPOSE: To perform the waveform shaping with no malfunction due to the waveform defects or noises by synthesizing the outputs of a phase shift circuit in response to the frequencies of two basic wave components to produce the signals having an approximately equal phase shift amount to both frequency components and correcting the attenuated degree of said signal to compare this signal with an input signal.

CONSTITUTION: A resistance R2 and a capacitor C2 form the 1st phase shift delay circuit with a resistance R3 and a capacitor C3 forming the 2nd phase shift delay circuit respectively. A differential amplifier is provided with resistances R4∼R7 and an operational amplifier OP1. The differential amplifier delivers the voltage obtained multiplying the voltage obtained by subtracting the output voltage of the 2nd phase shift delay circuit from that of the 1st phase shift delay circuit by the gain of the differential amplifier. While resistances R8 and R9 and an operational amplifier OP2 form a phase shift inverting circuit. A comparator COMP2 compares an input signal IN2 with the output CIN2 of the phase shift inverting circuit for execution of the waveform shaping.