Sheet binding processing apparatus and image forming system

An image forming system comprising:

• an image forming unit configured to form an image on a sheet;
• a sheet insertion port through which a sheet bundle formed of a plurality of sheets is inserted;
• a binding unit configured to bind the sheet bundle inserted through the sheet insertion port;
• a detection unit configured to detect, at a predetermined detection time interval, an existence or non-existence of the sheet bundle in the sheet insertion port;
• and
• a control unit configured to stop, in a case where the non-existence of the sheet bundle is detected by the detection unit after the detection of the existence of the sheet bundle by the detection unit and before the binding of the sheet bundle by the binding unit, the operation of the binding unit without completing the binding process performed by the binding unit.