Abstract: A loose-leaf binder comprising, in combination, a first back strip having a plurality of split ring halves formed upright at given intervals along the outer edge thereof and a second back strip having similar ring halves formed along the outer edge thereof opposite to that of the first strip and adapted to engage end to end with the halves of the first strip. The first and second back strips are formed as discrete members separable from the combined state and have first and second lock members, respectively, at the both ends thereof in such manner that the lock members can engage with each other when the two strips are put together in the closed position. The two back strips also have, respectively, a first and a second sliding surfaces slidable relative to each other, and a first and a second guides extending substantially at right angles to the longitudinal directions of the two strips and formed to shapes complementary to each other so as to guide the sliding surfaces.