An image processing apparatus comprises: an image input unit to input an image; an image thinner for getting the OR of (m dots in the vertical direction)×(n dots in the horizontal direction) for the input image from the image input unit, thereby thinning out the (m×n) pixels and newly forming one pixel; a labeler for adding labels every line to black pixels of the image which was thinned out by the image thinner and adding the same label to the pixels which are continuous in the vertical, horizontal, or oblique direction and simultaneously tracing a rectangle; and a separator detector for distinguishing a rectangle corresponding to a sentence portion, a rectangle corresponding to a figure or photograph, a rectangle corresponding to a table, a rectangle corresponding to a separator, and the like by using a width, a height, an area, and a pixel density (the number of pixels to the area) of the rectangle added with the label by the labeler. On the basis of the result of the detection of the separator detector, the area of the input image is divided.