Abstract: A radio frequency IC includes a PLL circuit and prevents a PLL loop from being easily unlocked upon fluctuation of VCO oscillation frequencies due to a change in temperature. The PLL loop includes a VCO capable of switching oscillation frequency bands, a variable frequency divider, a phase comparison circuit, and a loop filter. A switching switch can apply one of plural predetermined set voltages to the VCO in place of a voltage of the loop filter in an open state in which the loop filter is disconnected from the VCO. The radio frequency IC als has a decision circuit that decides whether the phase of output of the variable frequency divider is ahead of or lags behind that of a reference signal of a predetermined frequency, and an automatic band switching circuit that generates a signal for switching VCO frequency bands, based on output of the decision circuit.