3 a as a chemical chamber is charged with the chemicals 4 a portion of the inner hole 3 a at the vessel 2 side is sealed by the first sealing plate 6 the first sealing plate 6 is made of for example a stainless sheet and is fixed to the end surface of the head block 3 at the vessel 2 side by welding the first sealing plate 6 is provided with a substantially hemispheric bulging portion entering the inner hole 3 a to endure the pressure of gas from the gas storage chamber 8 the bulging portion may be provided with a rupture promoting groove the initiator 5 is disposed to face a portion of the inner hole 3 a opposite to the vessel 2 the initiator 5 includes igniting chemicals and an ignition device such as a resistance heating element for igniting the igniting chemicals in the initiator 5 when power is applied to the ignition device the igniting chemicals react to generate a high temperature gas the initiator 5 is held in an end sleeve 3 b of the head block 3 by an initiator holder 11 the other end of the vessel 2 is provided with a guide hole 12 and the gas outlet 10 is disposed at the end of the guide hole 12 the second sealing plate 9 is provided so as to seal.