To enable the elimination of a primer coating process and the separation in recycling by integrally forming a plurality of projections that project in an inclined direction relative to the surface of a base material so as to lock to formed polyurethane.

Four projections 12 are formed integrally on the surface of a base material 10, arranged radially at intervals of 90° and in such a manner than the confronting projections protrude in opposite directions as well as in an inclined direction, and a pair of projections 13 disposed between groups of four projections 12 and register openings 11 in such a manner as to project in opposite direction as well as in an inclined direction. In foam molding, foamed polyurethane is formed on the periphery of the projections 12, 13 and locked to the base material 10. The inclined directions of these projections 12, 13 are various, and therefore even when external forces are applied thereto in every direction, they can hold the foamed polyurethane securely. In addition, when the inclined direction of one of these projections 12, 13, for instance, of the projection 12a, 13a, coincides with a direction in which a mold is released, the mold can easily be released. Even if the directions do not coincide with each other, the mold releasing can be facilitated by the flexibility provided just after foam molding is completed.