An image forming apparatus including: a print part; a feeding part; a first sheet feeding tray; and a second sheet feeding tray. The first sheet feeding tray stores a sheet of a first size therein, the feeding part feeding the sheet of the first size from the first sheet feeding tray to the print part in a sheet feeding direction. The second sheet feeding tray is mounted on the first sheet feeding tray and stores a sheet of a second size smaller than the first size therein, the feeding part feeding the sheet of the second size from the second sheet feeding tray to the print part in the sheet feeding direction, the second sheet feeding tray receiving a sheet printed by the print part and discharged in a direction opposite to the sheet feeding direction. The second sheet feeding tray has a pair of side guides which are provided in parallel to the sheet feeding direction and which contact against side ends of the sheet of the second side to guide the sheet of the second side to the print part. At least one of the pair of side guides is provided with a plate part which extends from an upper edge of the side guide to the other side guide and which receives the printed sheet thereon. The plate part has a backward-feed prevention part which prevents the printed sheet from being fed to the print part again.