PURPOSE: To secure the synchronization of a PN signal by catching the synchronization of the PN signal in the early stages with use of a correlation signal and an error signal.

CONSTITUTION: The received SS signal is inputted to a semi-synchronous detection/AFC circuit 100. Thus the semi-synchronous detection is carried out and a complex base band signal is outputted. This base band signal is inputted to a complex correlator 102 where the correlation is taken between the base band signal and a PN signal. Thus a complex correlation signal is obtained and inputted to a demodulation processing circuit 104. Then the complex correlation signal is latched synchronously with repetition of the PN signal and demodulated in accordance with a demodulation system. Thus it is possible to secure the synchronization of the PN signal despite the large frequency of a local carrier wave.