An image forming apparatus includes an image forming unit configured to form an image onto each sheet, an ejection unit on which the sheet is ejected, a sorting unit configured to sort the sheets ejected on the ejection unit into subsets, and a control unit configured to, when executing a mode for forming images on first sides of the sheets, ejecting the sheets with the images on the first sides, and forming images on second sides of the ejected sheets manually placed on a feeding unit for second-side image formation, control the sorting unit to sort the ejected sheets after first-side image formation into subsets so that the number of sheets in each subset does not exceed a maximum number of sheets stackable on the feeding unit.