PURPOSE: To provide compatibility for decoders by classifying picture elements of a screen whose aspect ratio is 16:9 into picture elements of a basic screen whose aspect ratio is 4:3 and picture elements of an additional screen other than the basic screen, and providing a block processing means, a high efficient coding means and a format processing means to the coder.

CONSTITUTION: A screen whose aspect ratio is 16:9 is separated into a basic screen in the middle whose aspect ratio is 4:3 and an additional screen at both ends other than the basic screen section, a block processing section 2 extracts a prescribed quantity of picture elements from both of the screens to form one block. An orthogonal transformation section 3 applies orthogonal transformation to data in the block, the data is inputted to a variable length coding section 5 via a data quantity control section 4 and subjected to variable coding and given to a basic screen format processing section 6 in which the data is subjected to format processing. Then an additional screen format processing section 7 inserts a data of the additional screen section to a part remained by the basic screen format processing and the result is outputted to an output section 8. Thus, the data is decoded simply even by a 4:3 exclusive decoder and a 16:9 exclusive decoder.