An air bag system M includes an air bag 40 which can cover a front surface 1a side of a front pillar 1 of a vehicle V, an inflator 55, an air bag cover 65, a case 61 which stores and holds the air bag and the inflator and holds the air bag cover, and bolts 59 which are provided so as to extend from the case for mounting the air bag system on to an installation portion of a front side door 11. A portion of an outer reinforcement 19 which reinforces an outer panel 18 of the front side door is configured as a mounting portion 20 of the front side door where the bolts are attached, and the air bag system M is installed at a portion of the front side door which lies in proximity to a belt line 14 on a side facing a vehicle's outer side by the bolts 59 being attached to the mounting portion 20 on the outer reinforcement.