PURPOSE: To accurately reproduce a picture size even when an original picture size is not an integral number of multiple of a block size to be processed in the picture storage device processing the picture in the unit of blocks and executing compression/expansion.

CONSTITUTION: When the size of a picture inputted from an external device 100 is not an integral multiple of a block size to be processed, a block processing circuit executes round-up processing to attain block processing the picture into a picture whose size is an integral multiple of the block size including the original picture. Then a companding circuit 105 applies companding to the picture subjected to blocking in the unit of blocks. After the picture is restored to a picture of an integral multiple of the block size once by a raster processing circuit 108, a mask circuit 109 masks the size of the original picture to eliminate undesired picture elements. Thus, the picture size is accurately reproduced.