An AGC unit 111 starts a gain control of the variable gain amplifying unit 102 when a bit saturation occurs in the digital baseband signal output from the A/D converting unit 104, and starts a gain control of the variable gain amplifying unit 102 when a detection of STS from the digital baseband signal output from the A/D converting unit 104 is started. The AGC unit 111 performs the gain control of the variable gain amplifying unit 102 once when the detection of STS is started, and performs the gain control of the variable gain amplifying unit 102 twice when the bit saturation occurs, namely a larger number of times than when the detection of STS is started.