To secure sufficient rigidity and to avoid an occurrence of sinking or the like during molding even when integrally forming a mounting member for a car body such as a rear spoiler by injection molding.

In this mounting member for a car body, a mounting member body (a spoiler body 10) and a reinforcing part 12 coupled by a hinge 14 to this mounting member body substantially throughout its whole length are integrally formed by injection molding. The reinforcing part 12 is bent toward the mounting member body by the hinge 14, and a part (a tip 12a) of the reinforcing part is fixed to this mounting member body.