To provide an image forming apparatus capable of preventing the generation of paper jamming due to a full state of a second paper discharge tray in dual-sided printing.

The image forming apparatus includes: a switchback roller for switching back a sheet to which an image is transferred by a transfer part and the image is fixed by a fixing apparatus; and a paper discharge tray to which sheets are discharged under the switchback roller and can perform dual-sided printing. In the dual-sided printing, a sheet whose one side is printed is carried by the switchback roller, the sheet is discharged to the paper discharge tray and fed again by inverting the switchback roller, images are printed on both the sides, and then the dual-side printed sheet is discharged to the discharge tray. The image forming apparatus is provided with also a full state detection means for detecting that the paper discharge tray is full of discharged sheet, to inhibit dual-sided printing.