Abstract: A differential detector (2) reproduces a spreading code (S2) of a received signal (S1). A digital correlator (4) calculates a correlation value between the reproduced spreading code (S2) and a reference spreading code (S3) by collating bit by bit. The timing when the correlation value exceeds a predetermined threshold value (D2) means that the reproduced spreading code (S2) and the reference spreading code (S3) match in phase. A phase of the reproduced spreading code (S2), or a phase of the received signal (S1), is discriminated at that timing. A multiplier (8) outputs a modulated signal (S6) by multiplying the received signal (S1) bit by bit in phase by a spreading code (S5) which has the same code as the reference spreading code (S3). In result, a spreading code with an accurate code sequence and phase is obtained for despreading, and theoretical process-gain is obtained.