To vary a shifting amount of overlapped sheets upon sort discharge from that upon non-sort discharge in a device always discharging double sheets.

During sort discharge having a tip abutting member, the shift amount of the sheet is set at substantially 0 mm to prevent a hit trace or a scar in butting the sheet on the tip abutting member. During non-sort discharge (having no tip abutting member), the lower one of the overlapped sheets is shifted upstream in the conveying direction to prevent a returning failure of the discharged lower sheet.