In a post-processing device (sheet discharge device), a pile thickness calculating section calculates, from a type and the number of paper sheets discharged through a sheet output port, a thickness of a pile, at its leading end, of sets of paper sheets on a sheet output tray (piling section), calculates a thickness of the pile, at its trailing end, of sets of paper sheets on the sheet output tray from an amount of movement of a lifting section, and calculates an angle of inclination of the uppermost set of paper sheets in the pile from the thicknesses of the pile at its leading and trailing ends, a height of inclination of the sheet output tray, and a length of the paper sheets. The control section controls the sheet discharge section to change a manner of discharging a subsequent set of paper sheets according to the calculated angle of inclination.