An image forming apparatus includes a printer body having a developing portion and a fixing portion therein; a plurality of sheet feeding rollers successively disposed along a sheet discharge path of the printer body and driven to discharge a sheet from fixing portion to an upper portion of the printer body; and a rear cover portion having a rear cover provided on a side of the printer body to open and close, a guide rib member to guide the sheet from the fixing portion, an idle roller to rotate in contact with one of the sheet feeding rollers to feed the sheet, and a supplementary guide member to change a position thereof when the rear cover is open to prevent the sheet being discharged to the guide rib member from running into the idle roller.