A binding component includes ring back portions, first ring arm portions, second ring arm portions and a back part to which the ring back portions are connected. Each ring back portion, each first ring arm portion and each second ring arm portion forms an annular ring part. Each ring part includes fitting portions at places where the ring back portion and the first and second ring arm portions are connected. The fitting portions are configured to be fitted by an operation of opening and closing the first and second ring arm portions with hinge portions of the ring back portion. Each fitting portion includes at least one first fitting convex portion, at least one first fitting concave portion to engage with the first fitting convex portion, at least one second fitting convex portion and a second fitting concave portion to engage with the second fitting convex portion.