In the case in which an electrical connection between upper and lower layers is to be carried out through a via opening portion 16 provided on an insulating layer 14 of a wiring substrate constituting a multilayer wiring substrate, the electrical connection between the upper and lower layers is performed through a conductive material 30 while exposing a part of wall surfaces of the via opening portion 16 of the insulating layer without covering all of the wall surfaces of the via opening portion 16 with the conductive material 30.