Output paper stacking device of a printing apparatus and method for completing the same

An output paper stacking device includes a tray installed at a position lower than a paper discharge opening of a printing apparatus so that printed paper sheets discharged through the discharge opening can stack sequentially. Guide levers are installed to project upward through respective through slots provided in the tray for guiding both sides of the printed paper sheet, and for aligning the paper sheet at a predetermined position. A supporting unit for rotatably supporting the guide levers is provided so that one end of each guide lever can be balanced by another end of the guide lever in a state in which one end of the guide lever projects upward through the through slot of the tray. Thus, the output paper stacking device according to the present invention guides and aligns a paper sheet with guide levers having simple structures and which do not require any external driving power.