PURPOSE: To regenerate a clock whose phase synchronism is quickly pulled in and phase noise is small by providing a clock component extracting part, a reference clock generating part, a correlation part, a clock phase difference calculating part, and a clock output.

CONSTITUTION: A clock component extracting part 1 calculates a difference signal C1 between squares of I and Q signals Si and Sq after regenerating a carrier wave, and a reference clock generating part 12 outputs two orthogonal reference clocks C2 and C3 by a known clock frequency. Each correlation part 15 calculates correlation values C4 and C5 between the clock component C1 and two reference clocks C2 and C3. A clock phase difference calculating part 16 calculates a phase difference P2 by the operation of a prescribed formula and outputs it to a clock output part 20, and the output part 20 obtains a sum P3 of a reference clock phase P1 and the phase difference P2 to take a cosine component, and thereby, a clock CLK of the reception signal is reproduced and outputted. Thus, the clock phase synchronism is quickly pulled in, and the clock is reproduced with a small phase noise after pulling-in.