A vehicle includes an air bag device for an occupant seated in a rearmost seat. The air bag device includes an air bag, which is accommodated at the rear end portion of the roof of the vehicle in a folded state, and an inflator, which supplies gas to the air bag. The air bag is unfolded downward to be inflated between the rearmost seat and a rear window glass. The air bag device has several functions to effectively protect an occupant seated in the rearmost seat, such as a function to apply a predetermined tension to the inflated air bag, a function to properly restrict the thickness of the air bag, and a function to properly control the unfolding direction of the air bag.