PURPOSE: To ensure bridge mounting onto the rear body, etc., of a vehicle and increase the degree of freedom for the location of the grounding part by inserting an anchor bar in a receptacle hole in a high position surface through a through-hole provided in the top end of a bridge which is set over the high position surface and low position surface of a stepping part, and mounting the bridge rotatably within a plane.

CONSTITUTION: A receptacle hole admitting the insert part 1b of an anchor bar 1 is furnished at the rear end face of, for example, the rear body of a truck in such an arrangement as located identical to a through-hole 7 provided in a bridge 4, and the anchor bar 1 is set free from a mounting member and inserted in the receptacle hole upon passing through the through-hole 7, and thereby the bridge 4 can be mounted rotatably round the receptacle hole. As a result, the plane position of the bottom grounding part of the bridge 4 becomes free in sector form, and the location of the grounding part can be made any as desired. The mounting member 2 is welded fast to a stepping member 6 on the end plate 8 formation side, which liberates the anchor bar 1 nipped by the mounting member 2 from risk of falling or being left as it is.