A sheet stacking apparatus includes an alignment member to align a sheet stacked on a stacking tray in a width direction perpendicular to a direction in which the sheet is discharged. When stacking a plurality of sheets on the stacking tray, the sheet stacking apparatus lowers the stacking tray, so that a predetermined distance is maintained between the top surface sheet and a sheet discharge port. If the stacking tray is lowered to a predetermined position while the alignment unit is executing an alignment operation at a first position, the sheet stacking apparatus lowers the alignment member to a second position lower than the first position and causes the alignment member to execute the alignment operation at the second position.