PURPOSE: To efficiently coding even if the image area of a document has complicated structure which is not separated into a rectangular area.

CONSTITUTION: Image data is inputted to a picture element attribute deciding part 2 and decided whether it is a picture element in a gradation area or a picture element in a monochromatic area. At every area devided by an area dividing part 3, an area deciding part 4 decides color/monochrome and character/natural picture, background. A coding processing part 5 imparts an area number to each area, a header is constituted of the area number and an area attribution, and at every kind of area, coding data is stored in a memory 6. At this time the background and a base aren't coded.