The bottom wall (12) of a rectangular housing (10) comprises a trough-like depression (14) which is sealed on the inside of the housing (10) by a cover (22) provided with a securing flange (22A). A propellant charge (42) is introduced into the trough-like depression (14). The housing (10) is sealed at its front side by a covering formed by two pivotal foamed material plates (30, 32). In the interior of the housing (10) a folded gas bag (26) is accommodated which is inflated by the gases forming on combustion of the propellant charge (42) and flowing through gas passage openings of the cover (22) into the interior of the gas bag (26). Since the propellant charge (42) can be introduced directly or using a simple capsule housing of plastic into the interior of the trough (14) a separate and involved gas generator housing can be dispensed with.