PURPOSE: To realize an inexpensive FSK demodulator with no adjustment and with high reliability by providing a digital oscillator generating a reference signal and a digital phase comparator comparing the phase of the reference signal with an FSK modulation signal.
CONSTITUTION: A reference signal of a frequency fc=(f 1 +f 2 )/2 is inputted from a digital VCO 33 to a terminal R of a digital phase comparator 35. In this case, when a signal of a frequency f 2 (f 2 <fc) is inputted to a terminal V, the level of a terminal V 1 goes to '1'. When a signal of a frequency f 1 (f 1 >fc) is inputted to the terminal V, the terminal D 1 goes to '1', an RS flip-flop 37 is set and the output Q goes to '1'. Thus, a demodulation signal in response to a data is obtained from the RS flip-flop 37. Since the circuits constituting the titled demodulator are all digital circuits, no adjustment is required, the reliability is high and the cost is reduced.