An image forming apparatus includes: an image forming section; a discharger for discharging and guiding the copying paper to an outlet; and a controlling section for operating the image forming section, based on an image forming instruction from an operation section. A data fetching section fetches first image data on a plurality of pages and second image data on a plurality of pages. The operation section accepts, as the image forming instruction, a sheaf-unit sorting instruction which includes a predetermined number of copies of each of the first image data and second image data and sorting of the copies. The controlling section, based on the sheaf-unit sorting instruction executes, for the predetermined number of copies, an operation of guiding the first and second sheafs of copying paper, in sequence, to the outlet so that the first sheaf and second sheafs of copying paper are piled in order.