A sheet post-processing device includes a stacker section that temporarily stores paper sheets as a paper sheet bundle, a stopper that regulates a carrying-in direction leading end of the paper sheet carried into the stacker section, a binding section that binds the paper sheet bundle regulated in position by the stopper, and folding rollers and a folding blade that perform folding processing for the sheet bundle bound by the binding section at a predetermined folding position of the paper sheet bundle. The binding section binds the paper sheet bundle with a paper-made staple. The stopper sets a position of the paper sheet bundle such that a binding position of the paper-made staple straddles the predetermined folding position. With this configuration, there can be provided a sheet-post processing device capable of folding the staple together with the paper sheet bundle.