To reduce the size of a wheel arch unit and to improve appearance in an exterior part mounting structure of an automobile. In the structure, a second exterior part is fixed lapping on the side of the wheel arch unit of a first exterior part consisting at least of a part of the wheel arch unit of the automobile.

A mudguard 16 passes through a wheel arch unit 10 from the outside of a car breadth direction of a rear bumper fascia 14. It extends to a position opposite to a tire side from the tip 14b of both sides 14a of the rear bumper fascia 14 inside of a car breadth direction of the rear bumper fascia 14. The mudguard 16 is attached on a closing rear bumper bracket 20 extending along the car breadth direction to the rear bumper fascia 14 from a rear fender 18. The closing rear bumper bracket 20 and the mudguard 16 hold the rear bumper fascia 14.