The image forming apparatus sets, as a cutting area, an area containing an image of a double-page spread out of image data obtained by a scan of a book-type document, sets a borderline which divides an area corresponding to one page of the image data and an area corresponding to the other page of the image data from each other, and divides the cutting area cut out from the image data into a one-side area of the borderline and the other-side area of the borderline, thereby generating a first pre-output page in which divided image data of the one-side area is provided and a second pre-output page in which divided image data of the other-side area is provided.