The gas generator includes, a housing having a gas discharge port, a first combustion chamber defined by the housing, a first gas generating agent adapted to generate gas to inflate an air bag, the first gas generating agent having a first combustion temperature and disposed in the first combustion chamber, a second gas generating agent adapted to generate gas to inflate the air bag, the second gas generating agent having a second combustion temperature lower than the first combustion temperature and disposed in the first combustion chamber, and a first ignition unit for directly igniting at least one of the first gas generating agent and the second gas generating agent.