The present invention discloses BPSK demodulator, which uses a delay circuit to delay a BPSK signal and mixes the delayed BPSK signal with the undelayed BPSK signal to output a demodulated data signal, and which uses a phase rotation circuit and the demodulated data signal to obtain a carrier clock signal. The operating frequency of the delay circuit is the same as or 0.5 times the carrier frequency. Therefore, the present invention consumes less power and is realized by digital circuits and analog circuits.