A sheet processing device performs saddle stitching binding a bundle of stacked paper sheets, and includes a stacker section temporarily stacking conveyed paper sheets substantially vertically; a stopper regulating the paper sheets stacked in the stacker section; a first binding section provided in the stacker and saddle-stitching, with a metallic staple, a paper sheet bundle regulated by the stopper at a binding position around a center of the paper sheet bundle in a sheet conveying direction; a second binding section saddle-stitching, without using the metallic staple, the paper sheet bundle being regulated by the stopper at the binding position around the center of the paper sheet bundle in the sheet conveying direction; and a folding section folding in half the paper sheet bundle regulated by the stopper at a folding position at which the paper sheet bundle is bound by the first binding section or second binding section.