PURPOSE: To convert the RGB output of a personal computer into an NTSC system composite signal while the RGB output is compressed as a multiple of 5/6 in the vertical direction.

CONSTITUTION: An odd number line image memory 12 and an even number line image memory 13 having a storage capacity by 40 lines being a required minimum storage capacity are used and a write clock and a read clock whose speed ratio is 2:1 are used for read write and an odd number lines and even number lines of a read line sequential scanning component video signal are mixed by a prescribed ratio to compress the signal as a multiple of 5/6 in the vertical direction. Since the video signal by one line is synthesized by video signals of two lines, flicker or the like is suppressed by the filter effect attended with the synthesis.