to regulate the flow of the gas being fed into the air bag from the inflator. For example constructions such as providing one gas delivery opening in the middle of the diffuser to guide the gas into the middle of the air bag or making a gas delivery opening in the diffuser on the side of the gas blowout part of the inflator small and a gas delivery opening in the diffuser on the opposite side large to balance the amounts of the gas guided into the air bag flowing to the left and right are employed.
Thus, diffusers of the related art have been disposed in order to guide gas into the air bag uniformly in the width direction thereof, and have not positively controlled the shape ofthe air bag during its deployment by means of their gas delivery openings. Because of this, in air bag devices of the related art, to control the deployment behavior of the air bag, tear seams and tethers have been provided on the air bag itself, and consequently there have been problems such as that the package volume of the air bag is large and that the air bag is expensive.