A multilayer wiring substrate has a main face and a back face, and a configuration in which a plurality of resin insulation layers and a plurality of conductor layers are laminated. A plurality of conductor layers provided on the side toward the back face in relation to a resin insulation layer serving as a center layer are formed such that the average of their area ratios becomes greater than the average of area ratios of a plurality of conductor layers provided on the side toward the main face in relation to the center layer. A plurality of resin insulation layers provided on the side toward the back face are formed such that the average of their thicknesses becomes greater than the average of thicknesses of a plurality of resin insulation layers provided on the side toward the main face.