To reduce the deterioration of the productivity of print caused by the abandonment of staple waste from a staple waste collecting section of a stapler unit to a staple waste box.

A post-processing device includes a stapler unit 62 which is provided to be movable to a staple processing position for performing staple processing and an abandonment position for abandoning staple waste collected in a staple waste collecting section 70 to a staple waste box 61, and a control section for moving the stapler unit 62 to the abandonment position to abandon staple waste from the staple waste collecting section 70 to the staple waste box 61 when it is determined that the staple waste collecting section 70 is filled with the staple waste and when it is determined that it is before the staple waste in the stable waste collecting section 70 is full and prescribed abandoning timing not to hinder image formation.