An inflator for an air bag which can be assembled easily is provided. An igniter 30 is fixed inside a closure 20 using a resin 28 by charging molten resin through a resin charging hole 24 provided in the closure 20, and hardening the resin. The closure 20 is fixed to an inflator housing 12 by welding at a connecting portion 18. Since the number of components and the number of steps are smaller, favorable assembly workability is achieved.