A sheet stacker includes a sheet stacking member, a biasing force applier, an angle setter, and a regulator. The sheet stacking member has an upstream portion in a sheet conveyance direction. The upstream portion is movable in a vertical direction. The biasing force applier is configured to apply a biasing force to bias the sheet stacking member upward. The angle setter is configured to set an angle of the sheet stacking member in the sheet conveyance direction, relative to a sheet conveying portion, between a first angle and a second angle. The regulator is configured to regulate movement of the sheet stacking member in a case in which the upstream portion of the sheet stacking member is located closer to the sheet conveying portion at either the first angle or the second angle.