An airbag device may include a gas generator comprising: an initiator that is activated by an impact on a vehicle; an ignition agent that is ignited by the initiator; an ignition agent housing chamber that houses the ignition agent; a gas generating agent that is ignited and burned by the ignition agent; and a combustion chamber housing the gas generating agent. An airbag may be inflated by a gas generated by the combustion of the gas generating agent. Further, the ignition agent housing chamber is only partially filled with the ignition agent, thereby forming a space in the ignition agent housing chamber that is not filled with the ignition agent.