There is provided a coding apparatus in which an input image signal is divided into blocks, the block data is compression coded by using an orthogonal transformation, and (n) sync blocks are produced from the (m) compression coded block data, wherein each sync block has a first area in which important data in the orthogonal transformation coded block data of a specific number of blocks is arranged and a second area in which non-important data in the orthogonal transformaton coded block data of an unspecific number of blocks is arranged. There is also provided a decoding apparatus in which an image signal is divided into blocks, the block formed block data is compression coded, and the compression coded block data is decoded on an (m) unit basis (m is a natural number), wherein the apparatus comprises a first decoding unit for decoding the coding data of the inputted (m) blocks in accordance with the inputting order on a block unit basis, a second decoding unit for decoding the coding data of the inputted (m) blocks in accordance with the order opposite to the inputting order on a block unit basis, and an output unit for integrating the data decoded by the first and second decoding units and for outputting decoding data of the (m) blocks.