A wiring board including a first substrate having a penetrating hole penetrating through the first substrate, a built-up layer formed on one surface of the first substrate and including multiple interlayer resin insulation layers and wiring layers, the built-up layer having an opening portion communicated with the penetrating hole of the first substrate and opened to the outermost surface of the built-up layer, an interposer accommodated in the opening portion of the built-up layer and including a second substrate and a wiring layer formed on the second substrate, the wiring layer of the interposer including multiple conductive circuits for being connected to multiple semiconductor elements, and a filler filling the opening portion of the built-up layer such that the interposer is held in the opening portion of the built-up layer. The opening portion of the built-up layer has a tapered portion tapering toward the outermost surface of the built-up layer.