Provided is a sheet stacking apparatus including an aligning member lifting-lowering device configured to lift and lower aligning members between an aligning position where the aligning members abut to and align the sheets and a retreating position where the aligning members are lifted from an upper surface of the sheets, an aligning member moving device configured to move the aligning members in a sheet width direction, and a stack tray lifting-lowering device configured to lift and lower a stack tray based on a detection result of a sheet surface detecting device. A controller lifts the aligning members to the retreating position with the aligning member lifting-lowering device after the sheets stacked on the stack tray is aligned at the aligning position, and stops lifting-lowering operation of the stack tray lifting-lowering device while the aligning members are moved in the sheet width direction with the aligning member moving device.