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