PURPOSE: To obtain a high demodulation sensitivity by forming a pulse signal from n-set of frequency division signals obtained from frequency division of an input signal and synthesizing and smoothing the pulse signals.

CONSTITUTION: A limiter amplifier 2 shapes an FM signal inputted to an FM signal input terminal 1 and outputs the result to a 1/2 frequency divider 6. The circuit 6 outputs a signal applying 1/2 frequency division to the input signal at an output terminal 01 and a 1/2 frequency division signal having a phase difference by 180° from that of said signal is outputted at an output terminal 02. Monostable multivibrators 3-1, 3-2 output a pulse signal synchronously with the leading of the 1/2 frequency division signals at the output terminals 01, 02. A synthesis circuit 7 outputs logic 1 when both the two pulse signals is logic 1 or logical 0 and outputs logic 0 when one of them is logic 1. In smoothing the output waveform of the circuit 7 by an LPF, a DC is obtained and it is proportional to the change in the duty ratio of the input waveform, that is, the input signal frequency, then the circuit acts like an FM demodulator, Thus, a high demodulation sensitivity is obtained.