Gas is properly fed into a head facing portion while upsizing of an inflator is prevented. Throttle portions are provided for coupling between a frontal side and a backside of an airbag between a neck portion and a head facing portion. Seams are formed as contours of the throttle portions positioned outermost the airbag in a width direction. The seams are parallel to side edge portions, of the airbag positioned outside the seams in the width direction. Seams are formed as contours opposed to the throttle portions arranged adjacent to each other. The seams are approximately parallel to each other.