To ensure the consistent controllable flow of a fluid by tapering the end part of a rod part so as to easily rupture an interrupting means, and forming a number of grooves functioning as passages of a gas for expanding an air bag longitudinally on the rod part.

A high temperature gas generated by the explosion of an explosive 68 moves a shot body 62 from a retreated position toward a rupture disc 38. After the shot body 62 penetrates through the circular upper surface of an interrupting cap 46, the high temperature explosion gas partially breaks the side wall of an interrupting cap 46 through a space formed between poles 84 just before the tapered tip of the shot body 62 reaches the rupture disc 38. The high-temperature explosion gas flows into a pressure vessel 10 through the broken part of the side wall of the interrupting cap 46. Thereafter, the shot body 62 ruptures the rupture disc 38, and the gas within the pressure vessel 10 starts to flow into an air bag mainly through a groove 80 formed on the rod part 74 of the shooting body 62.