A gas generator for an air bag is provided with a porous tube member, in which a portion opposing the ejecting direction of a flame and the like generated due to an activation of an ignition unit stored in an inner cylindrical member is formed as a flame-preventing annular portion having no opening, disposed in a gas generator housing. Further, a multistage type gas generating apparatus prevents an erroneous connection between a plurality of igniter stored in a gas generator 1 and outputting portions of an ignition signal outputting device. In the multistage type air bag apparatus, the gas generator includes a plurality of igniters, and a defining unit for specifying the unique connection between the respective ignition signal outputting unit and the respective igniters is provided in a connector provided in a lead wire for sending an ignition signal to each of the igniters.