To immediately inflate an air bag without causing any pollution by sealing hydrogen and air separately in the predetermined spaces, mixing the hydrogen and the air when a seal is released so as to change them into a mixed gas composition within a detonation range, and igniting the mixture gas so as to discharge it in a detonating condition.

A space S is filed with pure hydrogen, and an opening 12 in a neck part 11 of a cartridge 1 is sealed by means of a sealing plate 13. On the other hand, an air cartridge 2 is filled with air so that the air and the hydrogen in the pure hydrogen cartridge 1 occupy 100% by volume when they are mixed together, and an opening 22 of a neck part 21 in the air cartridge 2 is sealed by means of a sealing plate 23. Electric current is let flow by means of a sensor 5b or a switch 5c, and gunpowder 40 is ignited so as to be detonated. By means of this explosion force, the respective sealing plates 13, 23 of the pure hydrogen cartridge 1 and the air cartridge 2 are opened, and the hydrogen and the air are jetted into a mixture combustion chamber 31 so as to be burnt by means of explosive heat of the gunpowder 40, and then, the detonated mixture gas is discharged from a discharge hole 34 toward the outside of the mixture combustion chamber 31, and as a result, an air bag 4 can be inflated at once.