PURPOSE: To obtain an excellent superimpose video signal by storing a binary signal obtained by extracting a change in a hue in a picture to a memory based on a color difference signal included in a color video signal, reading the storage content in the memory and replacing it with the video signal.

CONSTITUTION: Color difference signals R-Y, B-Y are binarized by differentiating circuits 46, 50 and Schmitt trigger circuits 48, 52 respectively. Outputs of an A/D converter 38, an R-Y signal binarizing circuit 40 and a B-Y signal binarizing circuit 42 are all given to an adder circuit 44. The adder circuit 44 adds inputted three binary signals logically and gives the result to a superimposing control circuit 32. Then a signal stored in the memory 34 via the superimposing control circuit 32 is similar to a signal inputted from the A/D converter 38. Thus, even when a picture whose luminance change is obscure is in use, excellent superimposing picture is obtained by a change in the hue.