Post processing apparatus and image forming system

A post-processing apparatus comprising:

• a binding device configured to bind a sheet bundle;
• a closing device configured to close an entrance to a binding position at which the binding device binds the sheet bundle;
• a driver configured to move the closing device to a closing position at which the closing device closes the entrance;
• and
• a changeover switch configured to perform switching to implement a state in which the binding device is able to bind the sheet bundle when the closing device moves to the closing position,
• wherein the closing device includes:
• an avoidance operation portion configured to move to the closing position to operate the changeover switch, and
• a drive coupler coupled to the avoidance operation portion to move the avoidance operation portion to the closing position by a driving force caused by the driver,
• wherein a coupling state between the avoidance operation portion and the drive coupler is released when movement of the avoidance operation portion to the closing position is prevented.