PURPOSE: To prevent beat disturbance from being caused even under the condition where the frequency band of an inputted modulation signal and a demodulated output is overlapped by interrupting an input signal of the modulation signal and an output terminal of the demodulated output by means of a digital operating circuit.

CONSTITUTION: An FM signal is inputted to an input terminal 21, an A/D converter 22 samples the inputted FM signal by using a sampling clock supplied from a clock generating circuit 23 so as to output a digital signal of a proper bit number. A digital signal corresponding to the demodulation output as to the input modulation signal is generated from the digital operating circuit 24, it is converted into an analog signal by a D/A converter 25 and extracted as a demodulation signal via an output terminal 26.