An AM demodulator includes an APC detection circuit that compares phases of an AM-modulated input signal and a signal output from a VCO. However, the APC detection circuit multiples the two signals before their comparison. As a result, even if the phases of the input signal or the signal output from the VCO is shifted by 180 degrees, the result of comparison by the APC detection circuit is not influenced by the phase shift. Moreover, when a signal detected by the AM detection circuit is in a potential range showing over-modulation, operation of a PLL circuit is stopped.