A fasten-on air bag device comprises an air bag housing which is attachable to the seat restraints and can be fastened-on by occupant; a crash sensing system for sensing and evaluating the crash data; an inflator installed inside the air bag housing, a plug-in signal-transmission receptacle and a detachable plug affixed to the air bag housing. By coupling with the plug-in signal transmission receptacle, the fasten-on air bag device can be utilized not only on the front seats but also the rear seats, and can be applied on all kinds of vehicles such as cars, buses, trains and airplanes. The direction of explosion is guided by the guiding core to assure the deployment of the air bag go outward and forward away from the occupant's body instead of aiming toward the occupant's body. In addition, the protective shield lining and the spread plastic lobes further protect the occupant's body. Therefore, the explosive expansion of the air bag would less likely cause harm to the occupant.