PURPOSE: To perform properly decoding of image data by eliminating fixed distortion of the part of a border line in area division in the coder performing motion compensation.

CONSTITUTION: Image data read from an image memory 201 are coded by coding sections 210, 211, decoded by local decoders 212, 213, block-processed by block processing sections 228, 229 and stored in image memories 208, 209. Motion detection sections 206, 207 perform motion detection by data stored in the image memories 208, 209 and since the image memories 208, 209 exchange data with each other and the image data of an adjacent area are referred to detect the motion. Since the image data of the adjacent area are referred to, distortion of the border part of the divided area is eliminated and a proper image is obtained at decoding.