A parallel scanning circuit outputs a parallel scanning signal for making forward and backward scanning lines parallel. A vertical correlation detection circuit detects a portion where the change in luminance in the vertical direction exceeds a predetermined value on the basis of a luminance signal, and outputs a movement control signal representing the distance of movement on the screen of the scanning line. A retrace period reversion circuit reverses the lime axis of the movement control signal in a retrace period. A clamping circuit clamps the movement control signal to a predetermined DC voltage at the timing of horizontal synchronizing signal. A synthesizing circuit synthesizes the parallel scanning signal and the movement control signal, and feeds a synthesized signal as a vertical velocity modulation signal to a vertical velocity modulation coil.