The sheet finisher includes a predetermined folding mode for receiving a sheet from a copy machine and which features a plurality of transfer guides through which the sheets received from the copy machine are selectively transferred; switching flappers for switching the flow of the sheet between guides, a temporary holding guide in which the leading end portion of the sheets can be temporarily inserted; a sheet folding arrangement including press roller pairs for folding the sheets; a sheet discharge angle control device which varies the angle at which the sheets are discharged onto an upper tray in accordance with the folding mode that is being used; a tray shift mechanism for moving the tray left and right so as to stack the sheets which are discharged thereonto in a classifying manner; a friction roller for moving a predetermined corner of each of the sheets into a preselected corner of the tray; a fastening device for fastening the sheets which have been maneuvered into the preselected corner by the friction roller; a tray rise mechanism for changing the distance between the upper surface of the tray and the level at which the sheets are discharged; an escape mechanism which drops processed stacks of sheets from the upper tray into a lower one; and a tray angle varying mechanism for changing the angle of the lower tray when the stacks are dropped theretowards.