A wiring substrate assembly includes a resin wiring substrate and a reinforcement member. The resin wiring substrate does not have a core substrate, and includes a substrate main surface, a substrate back surface, a laminate structure comprised of resin insulation layers and conductive layers, and connection terminals disposed on the substrate main surface, to which a chip component is connectable. The reinforcement member is bonded to the substrate main surface and defines an opening portion extending through the reinforcement member so as to expose the main-surface-side connection terminals. The reinforcement member comprises a composite material including a resin material containing an inorganic material.