Gas generator

The present invention relates to a gas generator particularly suitably used for expanding and inflating a side airbag for side collision or a passenger-side airbag. A gas generator S applicable to a side airbag or a passenger-side airbag. The gas generator S comprises an elongated cylindrical housing . The housing has, in its interior, a first combustion chamber , a third combustion chamber formed in a filtering member and a second combustion chamber which are formed in this order along an axial direction of the housing . The combustion chambers are each packed with gas generating agents that generate high temperature gas by burning, and ignition means for igniting only the gas generating agents packed in the first combustion chamber is disposed in a holder fitted in the housing