An image processing method includes inputting image data for one block line having pixels of N times of a minimum unit (MCU) of image compression in the direction of column, and the length in the direction of row equivalent to one length of a scanning line, and outputting sequentially the image data of each block by dividing the image data into a plurality of block, which consists of N units block arranged in the direction of column, each of the unit blocks consisting of M MCUs arranged in the direction of row. The output image data of each block is compressed from the upper side unit block of each block, and compressed image data for each block of one block line is obtained. The obtained compressed image data is written in the frame memory. The written compressed image data is changed in sequence.