An air bag apparatus is disclosed having a locking device which is adapted to prevent the inflation of a bag accommodated in an air bag body before the air bag body is mounted on a chassis, the bag being adapted to be inflated in front of a seat occupant when a predetermined acceleration has acted on the air bag body. This locking device is arranged such that an actuating member is driven by an operator's operation after mounting the air bag body on the chassis to release the locking device, thereby canceling a locked state and making the air bag body operable.
