An image forming apparatus has a tab sheet supply unit and a control unit. The tab sheet supply unit supplies tab sheets of an identical type from an identical sheet supply tray as a chapter tab sheet to be inserted at a breakpoint of a first level of classification of a document to be printed, as well as a section tab sheet to be inserted at a breakpoint of a second level that is a finer level of classification than the first level of classification. The control unit causes the tab sheet contained in the sheet supply tray to be discharged as an unnecessary tab sheet, if the tab position of the tab sheet to be supplied next from the sheet supply tray does not match with the tab position of the tab sheet to be inserted next during the printing of the document, until both of the tab positions match.