Patent ID: 7992867

Claim:
A sheet processing apparatus comprising: a stacking unit on which an ejected sheet is stacked; a moving unit which is brought into contact with an upper surface of the sheet stacked on the stacking unit so that the moving unit can slip and move the sheet in a direction which crosses a sheet ejecting direction; and a side edge aligning unit which receives a side edge along the sheet ejecting direction of the sheet when the sheet is moved in the crossing direction by the moving unit, wherein the moving unit further moves in a state where the sheet stacked on the stacking unit is in contact with the side edge aligning unit, and the sheet processing apparatus further includes a movement blocking unit which blocks the movement of the sheet which is moved to the side edge aligning unit by the moving unit, thereby allowing the moving unit to slip and move on the sheet so as to adjust a relative position with the sheet, and a controller which controls the movement blocking unit, wherein the controller allows the movement blocking unit to cancel the block of the movement of the sheet when the moving unit slips and moves by a predetermined distance.