1. An image forming apparatus which forms an image on a sheet, comprising: an image forming section to form images on sheets according to a plurality of page image data divided in a plurality of chapters; a finisher section for forming a book with the sheets divided in chapters; and a control section to combine heading image data with the page image data with respect to chapters in a matter that positions of the heading image data to discern chapters are along a fore edge of the book and to allow the image forming section to form the images when the book is formed by the finisher section.