A printed wiring board includes a core substrate, an electronic component accommodated in the substrate, a first buildup structure formed on surface of the substrate and including an interlayer insulation layer, and a second buildup structure formed on the opposing surface of the substrate and including an interlayer insulation layer. The substrate includes a core material portion including multiple resin layers, a first conductive layer formed on first surface of the core portion and a second conductive layer formed on second surface of the core portion, the core portion has opening through the resin layers and accommodating the component, the insulation layer of the first structure is positioned such that the opening of the core portion is covered on the first surface, and the insulation layer of the second structure is positioned such that the opening of the core portion is covered on the second surface.