To stabilize and ensure an operation of a ring binder for a long period.

In the ring binder having a constitution for transmitting a rotating force of a rotatably operating lever 7 to a slider 8 and taking place an operation contrary to folding in a concave manner and folding in a convex manner of operating plates 3A, 3B via the slider 8, a deflection deformable extended piece 91 in a thickness direction is provided substantially on an extension line of the slider 8, the piece 91 is vertically relatively immovably coupled to a site deviated from a pivotal point of the lever 7 to a cover 2 to a rotary end side, thereby directly converting the operation of the lever 7 to a protruding or retracting operation of the slider 8.