PURPOSE: To prevent occurrence of a case where the pattern displaying location on the picture is changed or disappears, by installing a means which controls the frequency of the vertical pulse signal.

CONSTITUTION: When a video signal exists, a defeat signal (c) is not inputted into a signal switching means 1 and a vertical synchronizing signal (a) is impressed upon a pattern setting means 2, and then, the said means 2 uses the signal (a) as a reset signal. When no video signal exists and the defeat signal (c) is inputted, the switching means 1 impresses a vertical pulse (b) upon the pattern setting means 2 as a reset signal through a frequency controlling means 3 having two frequency controlling means. The frequency controlling means 3 is composed of two sets of frequency controlling circuits. One of the circuits is controlled to prevent the flow of images in the vertical direction when a video signal exists, and the other is controlled to set the pattern displaying location on the picture. The pattern setting means 2 counts horizontal pulses (d) and sets the pattern displaying location in the vertical direction.