A reference member serves as a reference for aligning trailing edges of a stack of sheets stacked on a binding tray. A binding unit binds the sheets with the trailing edges aligned. A discharge unit discharges the sheets with or without performing the binding process from the binding tray to a discharge tray. The reference member is movable in a sheet width direction such that a first position of the reference member at a time of discharging the sheets without performing the binding process is closer to a center of the binding tray than a second position of the reference member at a time of discharging the sheets with performing the binding process.