A bumper main body has a pair of recesses into each of which a blank cap is disposed and fixedly and releasably held at its clipping portions by a first arm of a U-shaped leaf nut mounted on each of projections. The blank caps each have an outer surface flush with an outer surface of the bumper main body and a blind hole aligned with one of internally threaded flanged holes of the U-shaped leaf nut. The blind hole has a thin-walled closed end which is removed when a fastening bolt is screwed through the blind hole into one of the flanged holes to fasten a license plate to the bumper main body. The blind hole is alignable with the other of the flanged holes when the clipping portions are reversely attached to the leaf nut.