A wiring substrate is configured such that each of laminate portions provided above and below a substrate core includes insulating layers and conductor layers stacked alternately. Of the conductor layers of the laminate portions, signal line layers are treated with a silane coupling treatment, which is a surface modification treatment, so that each signal line comprises a flat surface. A roughening treatment is performed on the remaining conductor layers of the laminate portions such that the surfaces of these layers are roughened. This structure provides an advantage when high-frequency signals are transmitted through the signal line layers. That is, when each signal line comprises a flat surface, an increase in conductor loss due to the skin effect can be prevented. In addition, by means of chemical bonding attained through the silane coupling treatment, the reliability of adhesion between the signal line layers and the insulating layer is sufficiently attained.