Coupling spots are properly protected upon reception of gas pressure. A seam is possessed as a partition that partitions the interior of an airbag, and the seam is a coupling spot along which a frontal-side base fabric and a backside base fabric are coupled to each other. First and second reinforcing fabrics are provided on inner sides of the frontal-side base fabric and the backside base fabric, and the first and second reinforcing fabrics have remaining margins that are oriented toward the gas supply side in the downward direction rather than toward the seam, and each of the remaining margins functions as a shield wall against a flow of gas toward the seam.