An oscillator has an oscillator which comprises a first variable capacitor to adjust capacitance based on a first signal and a second variable capacitor to adjust capacitance, generates an oscillation signal having a frequency in accordance with the capacitance of the first variable capacitor and the second variable capacitor, an integer phase detector to detect an integer phase of the oscillation signal, a fractional phase detector to detect a fractional phase of the oscillation signal, a phase error generator to generate a fourth signal indicating a phase error of the oscillation signal, a first filter to extract the first signal in a predetermined frequency band, included in the fourth signal, and to output the first signal, and a second filter to extract the second signal in a predetermined frequency band, included in the fourth signal, and to output the second signal.