An airbag device includes an airbag and an inflator stored inside the airbag. The inflator includes an inflator body and a mounting member that protrudes from the circumference of the inflator body generally orthogonally to an axial direction of the inflator body. The airbag includes an insertion region via which the inflator is inserted into the airbag. The insertion region has a double wall structure of an outer panel and an inner panel, and includes one or more through holes that are formed through the outer panel and inner panel for receiving the mounting member of the inflator. The outer panel includes an outer slit via which the inflator is inserted into the airbag, and the inner panel includes an inner slit via which the inflator is inserted into the airbag. The outer slit and inner slit are so arranged as not to overlap or intersect each other.