PURPOSE: To absorb dimensional change due to thermal expansion and product dispersion from piece to piece cheaply without impairing the appearance by forming the end part of the body of side mud guard from a soft material capable of expanding and contracting in the longitudinal direction, and forming the mounting part to the car body from a hard material.

CONSTITUTION: The mounting part of an end part retaining member 9 to a rear body arch 1d is formed from a hard material to generate a hard part 10, while the other part is formed from a soft material and joined with adhesives upon being overlapped on the inner surface of the end part of the body 3a of a side mud guard to generate a soft part 11, and this is constructed in a single piece. The soft part 11 is located elsewhere than the hard part 10, i.e., between the joining surface side with the mud guard body 3a and the mounting surface side to the rear body arch 1d. This end part retaining member 9 formed from hard material is secured to the rear body arch 1d, and the end of the mud guard body 3a mounted to the lower part of the car body by the member 9 is held with possibility of expansion and contraction in the longitudinal direction.