In a sheet processing apparatus that, for example, sorts or staples sheets after image formation, when preceding finishing is not completed on a processing tray, a third sheet fed anew into a waiting tray of a sheet placing member configuring a sheet waiting unit, which temporarily puts a sheet conveyed thereto on standby, is stacked to be shifted such that leading ends of second and third sheets are located further on a conveying direction upstream side than a leading end of a first sheet. Consequently, longitudinal alignment in the processing tray after that is surely performed.