An image forming apparatus includes a document conveyance unit, an image reading unit, and a control unit that performs an area identification process for identifying, from among a plurality of specific areas in document image data, a specific area including an image corresponding to a page number. The control unit extracts, as reference image data, image data in the specific area identified in the area identification process from the reference document, extracts, as comparative image data, image data in the specific area identified in the area identification process from among a plurality of specific areas in the document image data of a comparative document having a reading order later than the reference document by an extraction interval number, and outputs a confirmation page including combined image data in which the reference image data and the comparative image data overlap. The extraction interval number is a prescribed integer multiple of 10.