A passenger-side air bag device is provided including a door comprising a cover body and a side wall portion extending downwardly therefrom. Lock legs are disposed on the cover body and are configured to lock the door to the inner circumferential edge of an opening portion of an instrument panel. A housing constructed and arranged to be fixed to a car body includes slot portions into which the side wall portion of the door is fitted, and pawl portions for locking the circumferential edges of the lock holes of the door side wall portion to thereby prevent the door side wall portion from coming off from the slot portion. Gaps are provided in three directions between the door and the housing to compensate for any misalignment between the door and the housing.