To enable segregation disposal or re-usage of a binder, by allowing a base of the binder to be attachable and detachable to/from a spine of the binder.

Holes 11A and 30 are formed on the spine 11 and on the base 13 which is fixed at the inside of the spine 11. The fixation position of the base 13 is determined such that the hole 30 and the spine hole 11A coincide by their locations with each other, and the base 13 is fixed at this position by a base fixator 14. The base fixator 14 is structured with a perpendicular portion 45B which is positioned inside the holes 30 and 11A, a hook member 43 having an outside edge portion 45A extended from the bottom end of the perpendicular portion 45B, and a rotating member 44 combined with the hook member 43. The base 13 and the spine of the binder 11 are joined together with the rotating member 44 and the outside edge portion 45A, by changing the position of the rotating member 44 to be approximately at a horizontal position while keeping the outside edge portion 45A to be next to the outside of the spine 11.