PURPOSE: To improve a design aptitude to automatic manufacture and assembling by providing a hold cup having ribs of a given number or more in an enclosure to tighten thermal contact between an auto ignition device and a gas generator.

CONSTITUTION: This enclosure 52 includes a hold cup 56 and a hold disk 58, while the hold cup 56 has an inside 60 holding an auto ignition material 54 and an outside 62 having six ribs 66 at even intervals. Even if one of the ribs 66 is deformed at the time of pressing an auto ignition device 50 into a gas generator 10, sufficient surface contact are kept by the other ribs 66. The hold cup 56 is cylindrical, and includes an axially extending flexible flange and a surface means formed with plural openings. Hot gas generated from the auto ignition material 54 flows into an ignition device assembly 26 through the openings to ignite a solid fuel gas generation material 34 so that the gas generator 10 functions. Thereby, high-precision manual labor is not required, and automatic manufacture is enabled.