Abstract: A demodulator for demodulating a phase shift keying signal to regenerate a data signal. The demodulator comprises a clock generator for generating three-phase clock signals which are of substantially the same frequency as a carrier frequency of the phase shift keying signal and 120.degree. out of phase from each other, phase difference detectors for detecting phase differences of the phase shift keying signal relative to respective three-phase clock signals, a timing extractor for producing a data clock signal by fetching the three-phase clock signals and detected phase differences, and a phase difference change detector for producing the data signal by detecting the presence or absence of a change of phase difference between portions of the phase shift keying signal corresponding to preceding and succeeding bits of the data clock signal.