PURPOSE: To change the phase of an output pulse waveform and to synchronize it with a reference signal, by repetitively applying other pulse waveform during one period of an input pulse waveform, in a system altering the phase of an output pulse waveform obtained through the frequency division of the input pulse waveform.

CONSTITUTION: An input pulse waveform A is inputted to a delay circuit 1 to obtain one-shot pulse waveform C delayed by a half period, and this is inputted to a pulse synthesizing circuit 2 to obtain a pulse waveform A' after being synthesized with the input pulse waveform A. When this pulse waveform A' is inputted to a frequency division circuit 3, a frequency-divided output pulse waveform B is obtained. Next, the output pulse waveform B and a reference signal D are inputted to a synchronizing discrimination circuit 4, and a gate signal E is outputted according to the phase difference of both of them if the synchronization of the two is taken, and fed back to a pulse synthesizings circuit 2 to specify the operating time of the pulse synthesizing circuit 2.