PURPOSE: To prevent fluctuation of a frame picture at the right and left of a screen even when no input television signal is given while an NTSC signal is displayed on a wide aspect monitor.

CONSTITUTION: A signal discrimination circuit 13 discriminates whether or not an input television signal is an existing signal or a non-signal based on a horizontal and a vertical synchronizing signal pulse separated by a synchronizing separator circuit 1. In the case of non-signal, a selector 14 gives a horizontal pulse from a horizontal pulse generating circuit 15 to a phase detector 2. Thus, a clock with a stable horizontal period is given from a frequency divider 4 to a horizontal pulse generating circuit 5 and a pulse period inputted to a frame signal generating circuit 11 is made stable. Thus, a stable frame picture is displayed to a prescribed position on the screen in the horizontal direction by the frame signal generating circuit 11.