Abstract: A sheet post-processing apparatus is arranged such that in the non-staple mode, the leading edges of the sheets transported from the transport rollers are directed so as to be sandwiched between the upper and lower discharge rollers by a movable sheet guide in a non-staple mode position and the sheets are discharged onto a stacking tray through the upper and lower discharge rollers. In the staple mode, the leading edges of the sheets is directed to a discharge opening formed between the upper discharge roller and the movable sheet guide by the movable sheet guide in the staple mode position so as to be dropped onto the staple tray. After being processed by the stapler, the sheets are pushed by a pushing member through the discharge opening onto the stacking tray.