A finisher is disclosed which is connected to a copying machine and possessed of a stapler which effects a stapling treatment on the sheets discharged from the copying machine and a binder which inserts the discharged sheets into a cover and binds by adhesion the sheets and the cover for bookbinding. This finisher has a memory for memorizing the stapling treatment or the binding treatment as a treating mode in advance, a staple sensor for detecting the existence of the staple, and a cover sensor for detecting the existence of the cover. When either of the sensors detects the lack of staple or cover, a feasible treating mode other than the unfeasible treating mode due to the lack of staple or cover in the treating mode memorized in the memory is executed prior to the unfeasible treating mode.