PURPOSE: To improve the S/N of a demodulated FM signal by using n-set of counters so as to count clock pulse numbers plural half periods shifted at an interval of a half period independently based on a half period of the FM signal thereby prolonging the count time.

CONSTITUTION: A zero cross detector 1 outputs a zero cross detection signal every time a carrier of the FM signal passes through a zero point. The signal is frequency-divided by a frequency divided 2, waveform-shaped and outputted as pulses shifted at an interval of a half period of the carrier and generated at each period. The pulses R1, R2 reset the two counters 3, 4 in timings shifted by a half period each, the count for one period of the counters 3, 4 is read in the timings shifted by a half period each by using the pulses R1, R2, the result is fetched in registers 5, 6, and an RS flip-flop is set/reset by the pulses. The counters 3, 4 count number of clock pulses included in the time for one period shifted by a half period each in the carrier of the FM signal and the contents are shifted by a half period each.