10 of course the inflator 70 may be installed inside the air bag cushion 10 the gas injected from the inflator 70 to the gas injection part 19 is supplied to the left and right chambers via the partition part 16 which partitions the left and right chambers at the rear side of the air bag cushion 10 reference numeral 17 denotes sewing lines which define the gas injection part 19 the sewing lines 17 of the gas injection part 19 will be described in detail with reference to fig3 in this context it should be understood that the well known retainer ring placed in the air bag cushion 10 for retaining the inflator 70 to the cushion 10 is not shown in fig2 at least one through hole 15 b see fig3 is formed in each connection part 15 to permit air to flow between the left and right chambers 11 and 12 the gas may be non uniformly supplied from the gas injection part 19 to the left and right chambers 11 and 12 and the expansion speed of the chambers 11 and 12 may be different the through hole 15 b allows the gas to be uniformly dispersed to both chambers 11 and 12 thus causing the chambers 11 and 12 to uniformly and symmetrically expand still referring to fig2 a tether 60 is provided on the front portions of the left and right chambers 11 and 12 and passes through.