To reduce the weight of a concrete slab, and to fix an embedded material surely on the surface of concrete by forming the embedded material from a synthetic resin foam and a sheet which covers the surface of the foam.

In an embedded material 1, a sheet 3 which covers the surface of a synthetic resin foam 2, at least on the lower surface of the foam 2, is not adhered to the foam 2. When a substrate for a concrete slab is obtained using the embedded material 1, before cast concrete being cured, the material 1 is mounted at a prescribed position on the concrete, and the concrete is to be cured. By the sure adhesion of the sheet 3 to the concrete, the embedded material 1 is fixed firmly to the concrete.