A binder 1A is provided with: ring portions 3A to be inserted into binding holes formed in sheets of paper to bind the sheets of the paper; and a spine portion 2A which is configured by a member independent from the ring portions 3A and to which the ring portions 3A are attached. Each ring portion 3A has a plurality of engagement holes 6A which are attached to the spine portion 2A and arranged in a longitudinal direction of each ring portion 3A, and is cut depending on the number of the sheets of paper to be bound. The spine portion 2A has engagement protrusions 5A corresponding to the binding holes in the sheets of paper and the ring engagement holes 6A at both ends of each loop-shaped ring portion are attached to the engagement portions 5A.