a display device having an on - screen display function receives an yuv video signal such as the camera video signal or broadcast video signal of yuv format from a camera or recording medium , receives an rgb - osd signal from a circuit device of another system different from this yuv video signal , causes a memory within an osd processor to store the osd signal , converts an rgb video signal resulting from converting the yuv video signal to a panel - matched rgb video signal synchronized with a display synchronization signal , reads a panel - matched rgb osd signal from the memory of the osd processor in synchronism with this display synchronization signal , composes those rgb video signal and osd signal , using an osd composer , and supplies the resulting rgb composite video signal and the display synchronization signal to a display panel .