PURPOSE: To make the output of a phase comparator stable with less power consumption and simple configuration by inputting an output fluctuation of the phase comparator to one terminal of a differential amplifier, detecting it by an error detection means, and inputting it to the other terminal of the differential amplifier.

CONSTITUTION: An input signal is fed to one input section of a phase comparator 102, a frequency division output resulting from frequency-dividing the oscillation output of a voltage controlled oscillator 107 by a frequency divider 103 is fed to the other input section, a phase error output is smoothed by a low pass filter 104, the frequency division output of the frequency divider 103 is inputted to a low pass filter 105, in which the signal is smoothed, and the outputs of the low pass filters 104, 105 are fed to one and the other input parts of a differential amplifier 106. The fluctuation of logical output level of the phase comparator 102 appears at the output of the frequency divider 103 as the similar fluctuation and then the fluctuation component does not appear at the output of the differential amplifier 106. Thus, the output of the phase comparator 102 is made stable with less power consumption and simple configuration.