There is provided a binder configured to bind a bound member by being struck out from a binding machine. The binder includes a substantially U-shaped base member that is plastically deformable, and a surface member that is provided on a surface of the base member. There is also provided a coupled binder including plural binders. Each of the binders is coupled to other of the binders on front and back surfaces thereof. The front and back surfaces of each of the binders are not provided with the surface member.