To facilitate attaching and detaching a friction body to a holder, and to substantially completely prevent fallout of the friction body from the holder.

A bending stop body D formed of an operating part D1 and a leg part D2 is rotatably held in a holding hole 14c. A bending stop part D2b is gradually reduced in lateral width toward the lower end like an isosceles triangle in a front view to be rectangular in a side view. The bending stop part D2b takes a bending stop position and a release position at each 90-degree rotation. Both sides of the bending stop part D2b face the inside surface of both flexible taking-out prevention legs 12b, whereby both flexible taking-out prevention legs 12b can be bent inward enough to take the release position, and the front and back of the bending stop part D2b respectively face the inside surfaces of both flexible taking-out prevention legs 12b, whereby inward bending of both flexible taking-out prevention legs 12b is limited to take the bending stop position.