To simply apply processing such as color space conversion to color image data at a high speed without increasing a data amount.

In the case that a red, green, blue RGB space is converted into a cyan, magenta, yellow, black CMYK space, a CMYK conversion circuit 6 converts the space by reducing a data amount and adopts a data form where data of a color are equally divided and the divided data are added to low-order bits of other colors distributingly. A color extract circuit 10 of a recording control section 8 decodes the converted data in a prescribed way to extract each color of CMYK.