PURPOSE: To reduce the required number of memories for storing image data by encoding and decoding MH/MR encoded data by blocks when the data are decoded into image data after the data are converted into MMR encoded data.

CONSTITUTION: A decoder 101 decodes ME/MR encoded data 105 which are divided into preset blocks by means of a controller not shown in the figure. Then the divided data are stored in a memory 102 as image data 106 by preset blocks and encoder 103 encodes the data 106. By encoding the data 106 in such a way that the image data 108 of the leading line of the data 106 are encoded into the encode data ill of the leading line of encoded data 107 by blocks and the data 109 of the next line are encoded into the encoded data 112 of the next line, and then, the data 110 of the last line are encoded into the encoded data 113 by blocks of the last line after the data of the other lines before the last line are similarly encoded, the number of fraction bits is obtained from fraction bits 114 and the encoded data 107 by blocks are stored on a disk 104.