PURPOSE: To demodulate an over-modulated AM signal.

CONSTITUTION: An input signal is squared by a square device 20. Then an output of a VCO 22 is squared by a square device 24 in matching therewith. The phases of the outputs of the square devices 20, 24 are compared at a phase comparator 26, and an output of the phase comparator 26 controls the VCO 22. Then a recovered carrier outputted from the VCO 22 and an input signal are multiplied by a multiplier 18, synchronization detection is implemented to obtain a demodulation output. In this case, a 180° rotation component of the phase of the carrier due to overmodulation transmission is eliminated by the square processing at the square device 20 and the phase comparison is attained.