An airbag is provided in which connecting belts extending from opposed surfaces of a left airbag section and a right airbag section can be connected easily to each other and which can be manufactured easily. In one form, the airbag is composed of four panels; an inside panel, a right outside panel, a left outside panel and a proximal panel. Connecting belts are connected to the inside panel. The respective connecting belts are each formed with an insertion portion by folding a cloth fabric having a pair of end sides at about a midsection thereof. Rod-shaped jigs are inserted into the respective insertion portions. In a state in which the connecting belts are overlapped, the jibs are fixed in parallel at a predetermined distance, and width control tethers are pulled in the directions away from each other. Accordingly, a tensile force is applied to the respective connecting belts, and hence a tensed flatly extended state is achieved. Therefore, the connecting belts can be stitched with respect to each other easily.