To further improve the convenience for users in file management by binding additionally through the other arbitrary means the papers once already bound with a binding instrument.

Preparing the first opening members 11_1, 11_2 having openings corresponding to two binding holes formed on paper etc. and then opening the region A1 where the third binding hole can be formed between the opening member 11_1 and the opening member 11_2 and connecting those by a connecting member 12, thus the paper bundle is first bound with the binding instrument 1 and can be bound further with other means.