Patent ID: 7318584

Claim:
A sheet processing apparatus, which is connected to an image forming apparatus that forms an image according to an image forming job, comprising: a sheet superposing device that temporarily retains at least one sheet of a plurality of sheets being conveyed and superposes the retained at least one sheet and a succeeding sheet; a stacking device that stacks thereon the sheets conveyed from said sheet superposing device; an aligning device that aligns the sheets stacked in said stacking device; a discharged sheet tray onto which the sheets aligned by said aligning device are discharged in a sheet bundle; and a controller that causes said sheet superposing device to perform a sheet superposing operation, wherein said aligning device aligns sheets stacked in said stacking device in units of at least two sheets, even if the sheets stacked in said stacking device are first discharged to said discharged sheet tray as a first sheet bundle for the image forming job, and wherein said controller determines which of the sheets are to be retained in said sheet superposing device, based on the number of sheets to be stacked as the first sheet bundle in said stacking device, so that said sheet superposing device does not convey the sheets to said stacking device in unit of one sheet, even if the sheets to be stacked in said stacking device are stacked as said first sheet bundle.