This invention relates to an air bag inflation gas generator and aims to surely retain the space between an igniter and an ignition agent of a gas generating agent pack and to surely caulk an end cap. This invention has a longitudinal cylindrical member having its both ends sealed by one end plate and the other end plate and a plurality of gas outlets formed in its outer periphery, a gas generating agent pack which is accommodated in the cylindrical member, accommodates a plurality of gas generating agents in the compiled state in the axial direction of a longitudinal cylindrical pack whose both ends are sealed with one end face and the other end face and has an ignition agent disposed close to the one end face, an igniter disposed at the one end plate of the cylindrical member, and an energizing member which is disposed between the other end plate of the cylindrical member and the other end face of the gas generating agent pack and energizes the gas generating agent pack toward the igniter side.