A wiring substrate includes a core substrate, and a build-up layer including conductor layers and insulating layers alternately laminated on the substrate and via conductors formed in the insulating layers, each insulating layer having a coating layer and a support layer stacked on the coating layer such that the support layer has surface on which a conductor layer is laminated and the coating layer is covering a conductor layer, each via conductor connecting two conductor layers through an insulating layer. The coating layer has a thickness greater than that of the support layer and includes inorganic filler at content rate of 65 to 85% by mass, and the support layer includes inorganic filler at different content rate such that thermal expansion coefficient of the coating layer is smaller than that of the support layer and the coefficients of the coating and support layers have difference of 30 ppm/° C. or less.