PURPOSE: To prevent the degradation in quality of a reception signal due to band limiting by limiting the amplitude of an FSK signal and dividing the frequency and discriminating the frequency of the frequency divided signal to output a signal indicating the level of data.

CONSTITUTION: The received FSK signal has the amplitude limited by a limiter circuit 1 and has the frequency accurately divided by the frequency dividing circuit of a binary counter 2 and is inputted to a frequency discriminating circuit 3. Thus, a conventional frequency converting circuit consisting of a local oscillating circuit 4, a multiplier 5, and a band selecting filter 6 is unnecessary, and the degradation in quality of reception data due to the output frequency deviation of the local oscillating circuit 4 is prevented.