A wiring substrate includes a core layer having a penetrating hole, a first insulating layer disposed on a first surface of the core layer and having a first opening at a position of the penetrating hole, the first insulating layer containing no filler, a penetrating electrode disposed in the penetrating hole and in the first opening, and a first wiring layer laminated both on the first insulating layer at a first surface thereof facing away from the core layer and on an end face of the penetrating electrode, wherein the first surface of the first insulating layer and the end face of the penetrating electrode are planarized.