PURPOSE: To omit a multiplier and to simplify the constitution of a circuit demodulating a received modulated wave signal by turning on a switching circuit only when a specific phase relation is decided.

CONSTITUTION: A specific phase relation between a received signal (a) and a reproducing reference carrier signal is decided by a logical circuit such as a gate circuit 15, the error voltage of the specific phase relation is integrated by an integrator 16 through a switching circuit 17 and the integrated value is used as a control signal of a phase shifter 13. Even if any area is selected, the error voltage corresponding to the phase shift can be obtained, so that a reference carrier signal can be easily controlled to an optimum phase.