Sheet processing apparatus and image forming apparatus

A sheet processing apparatus comprising:

• a stacking unit on which an ejected sheet is stacked;
• a moving unit which is come into contact with an upper surface of the sheet stacked on the stacking unit so that the moving unit can slip and moves 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 which 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 so as to be away from the side edge aligning unit has been moved to and has been come into contact with the side edge aligning unit,
• 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 block cancelling unit which allows the movement blocking unit to cancel the block of the movement of the sheet, and
• the block cancelling unit calculates a position adjustment slip movement distance from a slip start position of the moving unit to a slip end position as a position away from the side edge of the sheet based on information of the sheet, and when the moving unit slips and moves by the position adjustment slip movement distance, the block cancelling unit allows the movement blocking unit to cancel the block of the movement of the sheet.