PURPOSE: To obtain a synchronizing clock signal stably by providing a means generating a triangle wave synchronously with a reference clock signal, a means comparing the wave with a reference voltage, a means measuring a phase of the synchronizing signal, and a means controlling a phase of the reference clock signal to the generator.

CONSTITUTION: A picture clock is given to a triangle wave oscillation circuit 104 subordinate to the generator and provides an output of a triangle wave of a picture clock frequency and a triangle wave voltage is given to level comparators 105-108. A reference voltage is given respectively to the comparators 105-108, and its voltage level is divided into five equal parts of a maximum voltage of the triangle wave. Thus, 5-bit information being the sum of outputs of the comparators 105-108 and an output signal of an oscillator 103 represents phase information of the picture clock. Moreover, information of C1-C4 is given to a phase measurement circuit 109. The circuit 109 latches the 5-bit information with a BD signal being a synchronizing input signal to measure a phase difference between the clock signal and the BD signal.