An air bag system of the invention is attached using an attaching piece portion and includes an air bag which is inflated for deployment when an inflating gas flows thereinto. The air bag is attached to an inner panel by attaching an attaching bracket having a pair of strengthening plates provided on front and back sides of the attaching piece portion with a bolt as a fastening means. A through hole in the attaching piece portion is set to such a size that a location constituting a circumferential edge is disposed at a position deflected from an area between a head portion of the bolt and the inner panel when a fastening stem portion of the bolt is fastened to the inner panel. The bolt is fastened to the inner panel in such a state that only the attaching bracket is interposed between the inner panel and the head portion.