PURPOSE: To synchronize an external device such as a personal computer and other character pattern superimposing device or the like based on synchronizing signals by separating horizontal and vertical synchronizing signals included in a composite video signal obtained from an external television receiver and forming horizontal and vertical synchronizing signal synchronized with the external signals.

CONSTITUTION: An oscillating signal is frequency-divided into a 130fH signal by a 1/2 frequency divider 9 and fed to an H counter 10. This signal is counted by the H counter 10 and frequency-divided into 1/130 to form a horizontal synchronizing signal having a frequency of fH. On the other hand, a signal having a frequency of 2fH is fed to a V counter 11 from the H counter 10, the signal is frequency-divided into 1/525 to form the vertical synchronizing signal. Further, the V counter 11 is reset by an external vertical synchronizing signal obtained from a synchronizing separator circuit 4 thereby forming the vertical synchronizing signal in synchronizing with the external signal. The horizontal and vertical synchronizing signals formed by the H counter 10 and the V counter 11 are fed to a television receiver 1 and the personal computer 2 to synchronize the both.