Typical configurations of a sheet stacking apparatus, a sheet processing apparatus, and an image forming apparatus according to the present invention includes a discharging unit which discharges a sheet; a stacking member which stacks a discharged sheet; and a holding unit which is movably disposed along a stacking surface of the stacking member and holds an upstream end in the discharging direction of a stacked sheet, wherein the holding unit is moved according to changes in the upstream end position of the sheet in the discharging direction.