PURPOSE: To provide an air bag inflater of simple construction compared to conventional inflaters, and of construction in which no ignition delay is generated, and highly safe capable of positively igniting automatically even when it is heated from any position when it encounters flames, etc.

CONSTITUTION: In the air bag inflater, a gas generating agent laminated body is formed by laminating plural ring-shaped gas generating agent forming bodies, each of which has a hole in the center part. A first ignition chemical agent 7 and an ignition device 11 are arranged on one end face of the laminated body, and a second ignition chemical agent 9 is arranged on the other end face. Filters 2, 4 are arranged so as to surround the gas generating agent laminated body, and housed in an outer vessel 1.