An image forming apparatus which prevents lowering of productivity when sets of tab sheets are used in one print job. The apparatus includes first sheet feeding units storing tab sheets, and a second sheet feeding unit storing plain paper. The apparatus produces print products in each which at least part of each set of tab sheets and plain paper are mixed. A print job processor causes print products to be produced by repeating a sequence of processing for feeding the at least part of each set of tab sheets and feeding plain paper. The processor causes surplus tab sheets to be discharged which have not been used for the print products and remaining in the first sheet feeding units, after a print product is produced through sheet feeding from a last one of the first sheet feeding units in order.