An air bag device with improved initial restraining capability includes an inflator that provides for shortening the starting time for rising the pressure of an airbag and also the time required for the pressure to reach the maximum value. The inflator includes a propellant, an igniter for igniting the propellant, a combustion chamber in which the propellant is burned, a filter chamber in which a filter is accommodated, a partition separating the combustion chamber and the filter chamber, communication orifices formed in the partition for allowing the communication between the combustion chamber and the filter chamber, and gas ports for supplying inflating gas into an airbag, and further comprises aluminum films which are broken and open the communication orifices at a predetermined pressure inside the combustion chamber and air-tightly close the communication orifices until the pressure reaches the predetermined pressure.