enlarged sectional view of a portion 2 of fig1 b the stored gas inflator 10 comprises a pressure vessel 12 which has an elongated cylindrical profile and is filled with high pressure gas the gas in the stored gas inflator 10 is pressurized at a predetermined inner pressure pm the pressure vessel 12 is provided at one end in the longitudinal direction with a gas port 14 the gas port 14 is closed by a first burst shim 16 the first burst shim 16 is designed to be ruptured to open the gas port 14 when subjected to a pressure equal to or higher than a predetermined pressure value p 1 from the inside of the pressure vessel 12 the pressure value p 1 is higher than the pressure pm of the stored gas hereinafter this pressure value p 1 is called as u201c burst pressure p 1 u201d of the first burst shim 16 the inside of the pressure vessel 12 filled with high pressure gas is divided by a second burst shim 22 and a partition 24 into a small chamber 18 facing the gas port 14 and a main chamber 20 having a capacity larger than that of the small chamber 18 at the boundary between the small chamber.