PURPOSE: To provide an encoder and its method in which the quality degrading of an image is prevented by suppressing the production of a block texture in a reproduced image.

CONSTITUTION: A block segmenting device 2 segments any block of 4×4, 8×4, 4×8 and 8×8 picture elements from an image stored in a frame memory 1. A mean value calculation device 4 obtains a mean value (DC component) of picture elements of the segmented block and a mean value coder 6 codes the mean value. A block segmentation device 3 segments a block of 8×8 picture elements from an image stored in the frame memory 1. The picture elements of the segmented block are subjected to DCT by a DCT device 5 and a DCT coefficient except the DC component is coded by an encoder 7.