A stacking unit accommodates sheets stacked on it. The stacking unit is capable of moving up and down within an operation range from a predetermined upper limit to a predetermined lower limit. A determination unit releases a determination of the fully loaded state if elapsed time from the time when the determination unit determines that the stacking unit has been fully loaded with sheets to the time when a sheet detection unit again detects an uppermost sheet of the stacked sheets as a result of the stacking unit being lifted up when the sheet detection unit can no longer detect the sheet after detection of the sheet exceeding a first threshold time preset in correspondence with the amount of curl imparted to the sheet.