To prevent that out of synchronism is apt to be caused as the S/N of an input signal is deteriorated.

A correlation arithmetic section 1 operates a transmitter side spread code a(t) included in an input spread spectrum(SS) signal, an output a(t+τ) of a spread code generating section, and an autocorrelation function R(τ). Let X be its peak value, then a converged value of the output peak is expressed as X/(1-α) by a cyclic filter 3 shown in figure B, where α is a filter coefficient (0<α<1). A synchronization circuit 4 acquires a phase of a spread code of received SS signal from the filter output and controls a timing of a spread code generating section 2 so as to trace the acquired phase. A noise amount arithmetic section 6 operated a noise amount Ny=(X'-X)/(1-α) included in the converged filter output peak value, where X' is the peak level of fluctuation when X is superimposed, and a filter coefficient adjustment section 7 adjusts the filter coefficient α in a way that the higher the noise amount Ny to the ideal converged value of the output peak X/(1-α) is, the more the ideal converged value is increased.