To make a flange portion small which restricts the turn of a connection pin.

A flange portion 19 which extends toward a direction intersecting with an axial direction of a connection pin 16 is provided in the connection pin, a protrusion insertion hole 20 protrudingly provided in the flange portion 19 is inserted to a protrusion 18 protrudingly provided in a bracket 12. Meanwhile, a stopper member 21 extending toward the width direction of the flange portion 19 is attached to the protrusion 18 using a retaining member 22, the flange portion 19 is sandwiched from the both sides of the width direction by contact portions 21C, 21D provided in the stopper member 21. Thereby, since the contact portions 21C, 21D in the stopper member 21 contact an upper end surface 19C and a lower end surface 19D of the flange portion 19, the turn of the connection pin 16 can be restricted. As the result, a stress by the turning force of the connection pin 16 does not concentrate to an inner side face of the protrusion insertion hole 20 protrudingly provided in the flange portion 19, the width of each end surface 19C, 19D of the protrusion insertion hole 20 and the flange portion 19 can be made smaller, and the flange portion 19 can be miniaturized.