A first structural material is bonded to a second structural material with a joining material provided with a mixed layer of a raw-material component for forming an intermetallic compound layer and a resin component that softens and flows during heat treatment interposed therebetween to form bonded structural materials. When the bonded structural materials are heat-treated, the first structural material is joined to the second structural material with an intermetallic compound layer, and the resin component exudes and covers the lateral circumferential (exposed) portion of the intermetallic compound layer with a resin film.