PURPOSE: To provide the system conversion device in which a natural video image after conversion even when a content of the video image is moved constantly in a vertical direction of a screen due to a tilt of a camera or the like.

CONSTITUTION: A control signal detection circuit 8 detects a control signal in a MUSE signal to extract a vertical motion vector included therein. A scanning conversion circuit 5 is provided with a memory, two coefficient devices and a coefficient control circuit and a vertical motion vector outputted from the control signal detection circuit 8 is given to a coefficient control circuit 54 in a scanning line conversion circuit 5. The coefficient control circuit generates a coefficient to be given to coefficient devices 52, 53 depending on the vertical motion vector.