In execution of aligning operation in a paper discharge device, every time the number of discharged print sheets reaches the number of aligning-start print sheets, a control unit performs aligning operation while the unit intermittently drives paper feed rollers of an image forming apparatus, to prevent discharge of a print-completed print sheet to a paper discharge table during aligning operation. Further, the control unit intermittently drives an elevation unit such that the print sheet on the top of a paper discharge table is always lower than a paper discharge position of a pair of paper discharge rollers. In execution of high-speed and high-volume printing, it is possible to perform alignment of the print sheet discharged on the paper discharge table without reducing productivity.