An operating member 3 has a shaft portion 31 and a fulcrum portion 32. A first swinging member 4 has a concave fitting portion 42. Inside the fitting portion, engaging surfaces and guide surfaces 45, 46 are included. The engaging surfaces are formed to be engageable with the fulcrum portion. The guide surfaces allow the fulcrum portion to swing with respect to the first swinging member. The second swinging member 5 includes an engaging portion 63 which includes a long hole, and which covers the fulcrum portion while passing the shaft portion through the long hole in a manner that the shaft portion is movable in the longitudinal direction of the long hole, in such a manner that the engaging portion and the fitting portion cooperate to sandwich the fulcrum portion. The engaging portion is coupled with the second swing shaft, and configured to be engageable with the shaft portion.