PURPOSE: To surely demodulate reception data even when it is hard to detect a correlation peak by an impulse noise, etc., by normalizing the integral of the square or the absolute value of the correlation value in a time window in which the correlation peak can exists, and demodulating the reception data from comparison between them.

CONSTITUTION: A transmission request signal RS is inputted to a timing generator 3, and a switch 6 is turned on by the output of the generator. The circuit 3 inputs a clock signal to PN sequence generators 1, 2, and outputs PN1 and PN0 sequence signals to a switch 5. Communication data SD is inputted to a synchronizing circuit 4, and the signals PN1 and PN0 are selected by switching the switch 5 corresponding to the output clock signal of the circuit 4, and outputs them to a transmission line 10 via the switch 6, an amplifier 7, a filter 8, and a transformer 9. Correlation is detected from the signals PN1, PN0 by correlators 24, 26, and those output signals and the output signal of a timing generator 38 are inputted to and integrated by integrators 33-36, and they are normalized by dividers 39, 40, and output difference is taken by a comparator 41, and the reception data RD can be decoded by processing circuits 41, 42. The circuit 42 outputs a carrier detection signal CD.