A braking member includes a body member and first and second interposed members. The first and second interposed members are detachably/reattachably mounted between a mounting groove and the body member. A braking force of the braking member is configured to be adjusted by attaching/detaching first and second projection members to/from first and second concave portions that are formed in a mounting groove so that the first and second projection members can contact the inner peripheral sides of the first and second interposed members.