To improve reduction of the weight of a steering component and a bottom bridge of a two-wheeled vehicle and facilitation of molding.

A bottom bridge 4 is molded of ductile cast iron equivalent to FCD380, FCD450, or FCD550 by casting, and reduction of the weight and facilitation of manufacture are achieved. In this case, when thinned wall parts 8, 8 by thinning the wall thickness of the intermediate part between the lower surfaces of arms 6, 6 laterally projecting from the center part of the bottom bridge 4, the wall thickness (c) of the upper wall 8c of the thinned wall part 8 is thinned by approximately 40 to 80% in comparison with the wall thicknesses (a), (b) of the front and rear walls 8a, 8b.