A sheet stacking apparatus, including: a conveyance unit configured to convey a sheet; a stacking unit on which a sheet conveyed by the conveyance unit is stacked, the stacking unit inclined downward in a conveyance direction in which the conveyance unit conveys a sheet and including a first region and a second region located downstream of the first region in the conveyance direction; a guide portion configured to guide a sheet conveyed by the conveyance unit over a sheet placed on the second region; and a pressing portion configured to press a sheet placed on the second region.