PURPOSE: To automatically correct phase difference by delaying a signal leading in its phase into plural pieces, and selecting the signal of the most suitable amount of delay according to the phase difference of two horizontal synchronizing signals.

CONSTITUTION: The output Y signal of a low pass filter 1 is inputted to a delay line 4, and it is sent to a selector 15 from output terminals 41 to 4n after being given plural prescribed amounts of delay. Besides, the outputs of the low pass filters 1,2 are inputted to synchronizing signal separation circuits 11,12 respectively, and respective horizontal synchronizing signals HY, HP separated here are phase-compared by a phase comparator 13. After the output of the phase comparator 13 during a definite period is measured by an integrator 14, the Y signal of the most suitable amount of delay is selected by the selector 15 from among the respective outputs of the delay line 4 according to measurement. Thus, after the Y signal and the signals PR, PB are corrected automatically in their phase difference and their DC components are made constant, they are converted from analog signals into digital signals by A/D converters 8, 9, 10.