To provide a method for surely selecting an optimum antenna from a plurality of receiving antennas in a short time in a selective diversity of a spectrum diffusion communication.

Antennas 1 and 2 are switched over during a period in which a signal is not received. A start of a receiving signal is detected in a slot 1. The same antenna as the antenna selected in the slot 1 is selected in a slot 2, and a mean value of the correlation value data of the signal receive via the antenna is acquired. The antenna is switched in a slot S3, and a mean value of the correlation value data of the signal received via the switched antennal is acquired. The optimum antennal is decided based on a result of comparing these two mean values.