A controller temporarily opens a pair of side fence plates under a prescribed condition to move the side fence plates away from both side ends of sheets in a sheet width direction, after each time stacking of sheets at a first or second sheet stacking position is completed, but before a sheet receiving tray is temporarily lifted down to offset an offset guide plate and an end fence plate. Else, the controller sets an amount of lifting up and down of the sheet receiving tray such that the amount at the second sheet stacking position is smaller than that at the first sheet stacking position when offsetting the offset guide plate and the end fence plate after each time the stacking of sheets at the first or second sheet stacking position on the sheet receiving tray is completed.