Case member of airbag device

A case member of an airbag device, comprising (i) a base plate portion 21 provided with a metal plate 31 and a stack portion having layers 32/33 made of synthetic resin which overlap both faces of said steel plate 31 and (ii) a peripheral wall portion made of synthetic resin which is integrally formed with each said resin layer, rising from the peripheral edge of the base plate portion and which surrounds the airbag in the retracted state. It possible to uniformly generate stress on both faces of the steel plate 31 in contraction at the time of molding while ensuring sufficient strength against the expansion pressure of the airbag, so that it is possible to suppress deformation in a cooling process after the molding and dimensional stability is high. The peripheral wall portion 22 is able to ensure sufficient strength even when it is integrally formed with each resin layer 32/33 of the base plate portion 21 in the form of a single layer.