An input signal is input via a first resistor to an inverting input terminal of an operational amplifier. A second resistor is provided on a feedback path between an output terminal and the inverting input terminal of the operational amplifier. A control voltage Vcnt output from the operational amplifier is input to a VCO. A frequency divider frequency-divides an output signal Sout of the VCO. A phase comparator compares an output signal from the frequency divider with a reference clock signal and outputs a voltage according to a phase difference. A loop filter removes a high-frequency component of an output voltage Vcp of the phase comparator and outputs the voltage to a non-inverting input terminal of the operational amplifier.