Gas generator for air bag

A cap member (85) adapted is to be disposed in a combustion gas discharge path of an air bag gas generator (10) and allows a combustion gas to pass therethrough while collecting mists contained in the combustion gas. The cap member (85) includes a hollow side wall (88) having a first end thereof open, and defining a plurality of vent holes (86) formed along a longitudinal direction of the hollow side wall (88), and also a ceiling wall (87) closing a second end of the hollow side wall (88) opposite to the first end.