A side air bag expands near a window at a time of collision of a vehicle to restrain an occupant from moving in a lateral direction. The air bag has an expansion duration .[.protracted.]. .Iadd.which is extended .Iaddend.to constrain the occupant during overturning of the vehicle. Stowability for stowing the air bag in a folded state in a side structure of the vehicle, such as a pillar and a roof side rail portion, is enhanced in that two woven fabrics are connected along an outer peripheral portion.Iadd., .Iaddend. to form a bag portion.Iadd., by .Iaddend.a textile structure woven using a common yarn .[.include in.]. .Iadd.of .Iaddend.both .[.fabrics.]. .Iadd.fabric sheets forming opposing sides of the air bag.Iaddend.. A whole of the bag portion is coated and sealed by an air .[.non-permeable.]. .Iadd.impermeable .Iaddend.coating material to improve air tightness. A mounting portion for mounting the air bag in the side structure, such as a pillar or a roof side rail, is integrally formed by extending the woven fabrics or the common-yarn textile structure portion outward from the outer peripheral connection portion, thereby improving stowability.