A saddle stitching portion which can bind the center portion in the conveying direction of a sheet bundle by a stapler and fold it by a pair of folding rollers and a pushout member, includes an end stopper which receives the downstream end of a sheet conveyed by a first conveying roller in a first receiving position on the downstream of the first conveying roller by a length not buckling the sheet on the downstream of the stapler or the downstream end of the sheet conveyed by a second conveying roller in a second receiving position on the downstream of the second conveying roller by the length on the further downstream, wherein the receiving position of the downstream end stopper is selected according to the length in the conveying direction of the sheet.