PURPOSE: To improve the transient response by detecting a frequency difference between an input signal and an output signal and controlling a variable frequency oscillating circuit directly so as to decrease the frequency difference when the difference is larger than a preset prescribed value.

CONSTITUTION: When a frequency difference between an input signal and an output signal is a prescribed value or below, variable frequency oscillation circuit 12 similarly to a conventional circuit generates a signal with the frequency in response to a signal of phase feedback control received from the output of a phase comparator circuit 4 operated with a phase difference of both the signals via an arithmetic circuit 4 and supplies the result to the phase comparator circuit 4. When the frequency difference exceeds the prescribed value, the variable frequency oscillation circuit 12 is controlled independently of the phase difference of both the signals and varies its output frequency so as to decrease the frequency difference. Thus, the phase synchronizing circuit with excellent response characteristic against the fluctuation of the input signal is obtained.