Disclosed is a paper processing unit for a binding device that can improve moving efficiency of a sheet of papers and prevent side binding error of the sheet of papers. The paper processing unit comprises a paper aligning unit including a tray stacking the sheet of papers, a rotational stopper provided at the end of the tray, stopping the sheet of papers stacked on the tray, and a paper clamp gripping the sheet of papers stacked on the tray and moving them to the paper finishing unit when stopping of the rotational stopper is released, and a binding carriage having a lifting unit structured to support the sheet of papers and adjust the angle of the sheet of papers depending on the binding position while the paper clamp moves the sheet of papers to the paper finishing unit and the binding process of the sheet of papers is performed, wherein the angle of the sheet of papers of which binding is finished is adjusted to move them to the position of the receiving stacker and an open tray is extended to the end of the tray to close and open.