Data, on which one page of original image data should be image-processed, indicates a first block image (G₁) constructed of continuous "n" lines of the original image, commenced from a top line thereof; and a second block image (G₂) through an M-th block image (G_M). Each of the second to M-th block images is comprised of continuous "n" lines of the original image, and overlapped portions for "d" lines are present between the first to (M-1)-th block images (G₁ to G_M-1) and the second to M-th block images (G₂ to G_M), respectively. With respect to each of the block images, (nW) pieces of pixel data indicative of this block image are supplied to an image processing circuit in both a column positional order and a line positional order, while the column position owns a top priority.