PURPOSE: To speedily form a slip-off preventing projection at least on a reinforcing cloth in a simple manner by superposing a plurality of reinforcing cloth on a base cloth in an installation part, without utilizing seaming, and to improve the close adhesiveness between the installation part of an air bag body and a base plate, suppressing the contact of the slip-off preventing projection with the base plate and to improve the operation reliability.

CONSTITUTION: An air bag body 11 having a gas injection port 15 is fixed on a base plate through a retainer. The air bag body 11 is formed by seaming the edges of a plurality of base cloth. The installation part 13 of the air bag body 11 is formed by superposing the reinforcing cloth 17a, 17b, and 17c on the base cloth. A slip-off preventing projection 19 is formed at least on the reinforcing cloth 17c at the position corresponding to the inside part of the retainer at the installation part 13 by the heating means such as ultrasonic cutter, etc.