The sheet processing apparatus is provided with: an apparatus main body that performs processing for a sheet; a sheet stacker on which a sheet transported from the apparatus main body is stacked in a first state where the sheet stacker is inclined with respect to a horizontal plane, and that is downwardly movable; and a moving-down unit that moves the sheet stacker down. The sheet stacker is provided so as to be detachable from the apparatus main body, and so as to change posture from the first state to a second state where the sheet stacker is less inclined relative to the first state.