PURPOSE: To provide a reinforce structure of an air deflector capable of improving workability and outer appearance and having joining strength and reinforcing rigidity.

CONSTITUTION: A material mixed with a glass mat and resin is press molded as in such a state as it is by filling it between a male mold and a female mold to make a shape of a collar part 4 of a reinforce 1 joined to a back surface of an air deflector 2 of an FRP material molded by an RTM molding method, etc., to be a shape matched to a joining surface of the air deflector 2. The reinforce 1 is not deformed in shape as it is hardened as it is pressed by the male mold and the female mold and becomes a single finished product. Additionally, the air deflector 2 and the reinforce 1 are both molded and treated of the FRP material by the RTM molding method, etc., and their composition plane is formed to be flat. Consequently, it is possible to improve joining strength.