SHEET PROCESSING DEVICE AND IMAGE FORMING DEVICE

PROBLEM TO BE SOLVED: To stably stack double folded sheets without enlarging an ejection tray by supporting a stacking means binding a plurality of sheets and discharging the bound sheets in the double folded form with the sheet folded side set lower than the opened side. SOLUTION: In a stacking tray 106, a part (projection part 106a) close to an ejection roller 104 is lifted above a stacking face 106b, and a bundle P of sheets are discharged so that its folded side is arranged on the stacking face 106b on the stacking tray 106 front edge side (ejecting direction downstream side) while its opened side is placed on the projection part 106a. In this way, the folded side is lowered below the opened side, so that a height difference between both sides can be reduced even when the folded side is swelled more greatly than the opened side. When the bundle P of sheets is thick, that is, when the folded side is greatly swelled especially, a sheet ejection speed by the ejection roller 104 is reduced so that the opened side of the bundle P of sheets is placed on the projection part 106a in the discharging process. When the bundle P of sheet is thin, a sheet bundle ejection speed by the ejection roller 104 is increased, arid the bundle P of sheets is discharged onto the stacking face 106b with the opened side prevented from being placed on the projection part 106a.