In a PLL circuit, a voltage controlled oscillator 4 has two voltage-current conversion circuits 40 and 41 and a selection circuit 42 for selecting an output of either one of the voltage-current conversion circuits 40 and 41. The output of the voltage-current conversion circuit selected by the selection circuit 42 is inputted to a current controlled oscillator 45. The one voltage-current conversion circuit 41 has an input thereof connected to an output of a loop filter 3, while the other voltage-current conversion circuit 40 has an input thereof connected to an input terminal 8 for evaluating the oscillation characteristics of the voltage controlled oscillator 4. As a result, time-varying fluctuations in the voltage of the loop filter resulting from a structure in which the input terminal for evaluating the oscillation characteristics of the voltage controlled oscillator is connected to the loop filter via a switch and time-varying fluctuations in the output frequency of the PLL circuit are effectively suppressed.