A file binder 103 has a back side plate member 2, a projecting member 3, and a front side plate member 6. A lower end part 5 of the back side plate member 2 is bent forward. The projecting member 3 projects forward from a part of the back side plate member 2 higher than the lower end part 5. The front side plate member 6 extends downward from a front end part of the projecting member 3 beyond a front end edge 80 of the lower end part 5, and forms a gap 81 from the front end edge 80. Pillar shape protruding portions 15 protrude backward from the front side plate member 6 under a lowermost end of the back side plate member 2, and beyond the front end edge 80, and reach the substantially same plane as a back surface of a main body part 4 of the back side plate member 2.