A sheet processing apparatus is disclosed. The sheet processing apparatus has a stacking unit configured to stack a sheet discharged from an image forming unit, the stacking unit including a stacker being configured to support a lower end of the sheet and a supporter being configured to support an under side of the sheet; a driver configured to drive the stacker along the supporter; and an opening configured for allowing removal of the sheet on the stacker to an outside; and a controller configured to control the stacker so that the stacker is driven to the opening along the supporter if a process is cancelled and if the sheet on the stacker needs to be removed.