PURPOSE: To provide a passenger air cushion module maintained while being held in a cylinder body by the action of a snap-attachment tool to the cylinder body provided in a cover during the time though an air cushion is unfolded through an unfolding door in response to the detection when detecting a collision of a vehicle.

CONSTITUTION: The necessity of a separate fastener is eliminated when installing a module cover 12 on a module reaction cylinder body 14, and a plastic module cover substantially integrally molded by injection molding is installed by fitting the fastener 30 to 38 to fasteners 16 to 19 of the module reaction cylinder body by snap-fit.