PURPOSE: To perform the initial catching of synchronism for PN signals, tracking, AFC operation and the demodulation processing of data with a simple configuration.

CONSTITUTION: A complex base band signal for one cycle of the PN signal is divided into three signals and inputted to correlators 34, 36 and 38, and the three divided PN signals are correlated. A total sum 46 of squares 40, 42 and 44 of absolute values outputted from these three correlators is calculated, and the synchronism of the PN signals is initially caught 50 by detecting the peak of absolute value square sum signals. A correlation signal corresponding to one cycle of the PN signal is provided by adding outputs from the three correlators 34, 36 and 38 and thus, data are demodulated 56. Since respective partial correlation signals outputted from the three correlators 34, 36 and 38 are provided with phase difference corresponding to frequency off-set, an error signal is provided corresponding to the frequency off-set by complex conjugate arithmetics 62 and 66. Thus, data demodulation, initial catching and error signal generation can be performed by a pair of partial correlators.