An image forming apparatus includes a sheet conveyance unit which conveys a long sheet having such a length as to extend at least from a sheet feed opening to a sheet output opening of an apparatus body, an image forming unit which transfers a toner image onto the sheet, a fixing unit including a heater to fix the transferred toner image, a temperature detector which detects a temperature of the fixing unit, and a control unit which controls the sheet conveyance unit in such a way that, when the front edge of the sheet is to be conveyed from the sheet feed opening to the sheet output opening with no toner image transferred onto the sheet, the front edge is prohibited from being conveyed into the fixing unit if the temperature of the fixing unit is higher than a first predetermined temperature.