A sheet processing device includes: a stacking unit configured to stack a plurality of sheets to obtain a sheet bundle; a stitched-sheet number acquiring unit configured to acquire a number of sheets in the sheet bundle, which is a target to be stitched; a permanent stitching unit configured to permanently stitch the sheet bundle; a temporary stitching unit configured to be capable of temporarily stitching a plurality of areas of the sheet bundle; a selecting unit configured to select any one of the permanent stitching unit and the temporary stitching unit to be used; and a stitching-process control unit configured to, when the temporary stitching unit is selected by the selecting unit, control the temporary stitching unit so as to change a number of areas that are stitched by the temporary stitching unit.