Abstract: A retainer ring having an air deflector, for use with an airbag mounting structure, includes a flange in which an inflater opening for receiving an inflater is formed; and a wall, a base of which is connected to the flange, extending upward and outward from the inflater opening at a predetermined angle to diffuse and deflect exploding gas upward. The wall, which realizes a simplified configuration for the retainer ring, may include convex portions projecting inwardly towards the inflater opening, being regularly spaced, and rib formations integrally formed on an inner side of the wall between the convex portions. The rib formations are evenly spaced, as a pair of rows covering the height of the inner side of the wall, and slope downward on either side of the convex portions. The airbag mounting structure clamps the inflater and the airbag between the retainer ring and a baseplate, which is mounted to a support within an automobile.