a wiring board comprises : a substrate having a surface on which a plurality of connecting electrodes are arranged ; an interposer provided with via conductors arranged so as to conform to an arrangement of a plurality of electrodes formed on an electrode forming surface of a semiconductor element to be mounted , so that , when the semiconductor element is mounted on the substrate , the respective electrodes of the semiconductor element are electrically connected to the respective connecting electrodes of the substrate through respective via conductors of the interposer . the interposer comprises a plurality of insulating layers stacked or laminated in thickness direction thereof , each layer having a plurality of filled vias penetrating in a thickness direction thereof , to form columns .