An air deflector device for a convertible vehicle has a deflector mounted to pivot between a shutting position, in which it participates in making up the roof when the roof is in its closed configuration, and an opening position that it takes up in order to protect the passengers inside the vehicle from the flow of air when the roof is in its retracted configuration. The deflector is mounted to pivot on a carriage which is itself mounted to move along longitudinal guides, it thus being possible for the effectiveness of the deflector to be significantly improved by moving the deflector along the longitudinal direction of the vehicle.