A sheet processing apparatus includes a discharge unit, a loading unit, an abutting unit, a support unit, and a control unit. The discharge unit discharges, from a discharge port, a sheet bundle transported along a transport path. The loading unit is loaded by the sheet bundle being discharged onto the loading unit. The abutting unit is disposed forward from the discharge port in a discharge direction of the sheet bundle so that the abutting unit abuts with a top surface of the discharged sheet bundle. The support unit is protrusible from and retractable into the discharge port and protrudes to an underside of the sheet bundle temporarily to support the sheet bundle when the sheet bundle is discharged. The control unit controls movement of the support unit such that the support unit reaches a position of the abutting unit after the sheet bundle abuts with the abutting unit.