An embedment member of a foamed resin article such as a seat pad formed in a mold. The mold is provided with engaging projections and a pocket portion formed in or on an inner surface of a core thereof. A surface of the embedment member is positioned to face the core and the surface is superposed onto the surface of the core such that the projections enter into large opening portions. Then, the embedment member is slid in such a manner as to introduce the projections into narrow portions and wide portions, thereby retaining the embedment member to the core. In this state, an end portion of the embedment member is fitted into the pocket portion. To release the foamed resin article from the mold, the foamed resin article is slid in a direction opposite to the direction of the aforementioned sliding.