In a communication semiconductor integrated circuit device, an oscillator (VCO 10) of a PLL circuit can operate in a plurality of frequency bands. With a control voltage (Vc) of the oscillator fixed to a predetermined value (VDC), an oscillation frequency of the oscillator is measured for each band to be stored in a storage (18). When the PLL operates, a setting value to specify a band is compared with the measured frequency values stored in the storage. As a result of the comparison, a band to be actually used by the oscillator is determined.