A pressing member is provided on a shutter member provided in a main body of an apparatus and adapted to open and close a folded sheet discharging port upon upward and downward shifting movement of sheet stacking means in such a manner that, after folding processing is performed by folding means as the shutter member is lowered, a sheet discharged onto folded sheet stacking means is pressed down by the pressing member. Further, if there is any sheet on the folded sheet stacking means, by stopping the sheet stacking means at a predetermined position where the shutter member lightly abuts against the sheet discharged on the folded sheet stacking means, the sheet is prevented from being pinched between the shutter member and the sheet stacking means.