Disclosed is a paper discharge apparatus of optimizing the moving path of a stapler provided at the rear of the paper discharge apparatus by effectively constructing the structure of the paper discharge apparatus that discharges paper onto a stacker tray. The paper discharge apparatus includes a pair of guide side plates including first rail grooves and curved cams adjacent to the first rail grooves, a pair of paper gripping units to grip the paper on the paper stacking plate in the contact with the curved cams, a first driving unit to drive the paper gripping units, an aligning stopper provided between the guide side plates to straightly move by a predetermined distance in the paper transfer direction from front end portions of the guide side plates, and a second driving unit to previously move the aligning stopper in the paper transfer direction just before the paper gripping units.