An image forming system superposes a plurality of recording sheets on top of another by a predetermined number of sheets and discharges the recording sheets. The image forming system includes a recording sheet conveyor, a recording sheet superposition unit, and a controller. The recording sheet conveyor conveys the recording sheets. The recording sheet superposition unit superposes a preceding recording sheet and a succeeding recording sheet sent from the recording sheet conveyor. The controller controls the recording sheet superposition unit not to superpose the preceding recording sheet and the succeeding recording sheet when the controller refers to recording sheet information of the preceding recording sheet and determines that the preceding recording sheet is a recording sheet of a specified kind.