A sheet processing apparatus of the invention includes a post-processing unit that applies post-processing to sheets supplied from an image forming apparatus, a conveying tool that guides the sheets subjected to the post-processing to a discharge port, a sheet discharge tray that receives the sheets discharged from the discharge port, and a control unit that controls an operation of the conveying tool and stops a discharge operation for new sheets, when a quantity of the sheets stacked on the sheet discharge tray reaches a full state set in advance. The sheet processing apparatus further includes a pressing unit that temporarily prevents movement of the sheet on the conveying tool, when a sheet is present on the conveying tool in the full state.