PURPOSE: To improve the phase noise of a phase locked loop circuit output by providing a frequency converter to convert the frequency of a VCO to a low frequency with a signal from a fixed oscillator.

CONSTITUTION: The output of a voltage control crystal oscillator VCXO4 is divided by a divider 5 and inputted to a phase comparator 6. On the other hand, the output of a VCO8 is inputted to a frequency converter 9 and converted to the low frequency by the signal of a fixed oscillator 10. A signal to be converted to the low frequency is divided by a divider 11 and inputted to the other terminal of the comparator 6. Here, detected both phase error signals are passed through a loop filter 7, which determines the response speed of a loop, and after that, sent to the VCO8. Then, the output frequency of the VCO8 is changed to a direction, in which a phase error is canceled. Thus, since the output frequency of the VCO8 is caused to be the low frequency at the input point of the divider 11, the frequency can be made small to the dividing number of the divider 11 and the phase noise can be improved in the output of the synchronizing circuit.