PURPOSE: To improve phase leading-in characteristics by shortening the discharge time of a capacitor for a low-pass filter sufficiently, by forming a short circuit by providing a transistor in parallel to the capacitor.

CONSTITUTION: Phase comparator 1 makes a phase comparison between output 6 of voltage control oscillator 3 and input signal 4 and generates control voltage 5 that corresponds to their phase difference. Control voltage 5, after passing through low-pass filter 2, enters voltage control oscillator 3. Oscillator 3 oscillates to generate output signal 6 synchronizing with input signal 4 in response to control voltage 5. Further, transistors Q1 and Q2 operating with gate signal 7 synchronize input signal 4 and output signal 6 with each other to prevent the deterioration of phase leading-in characteristics. Furthermore, transistor Q3 is provided in parallel to capacitor C2 of low-pass filter 2 to form a short circuit when Q1 operates, eliminating residual charge.