A wiring board includes an insulating board, a wiring sub board having a wiring layer, and an insulating layer. The insulating layer has a via hole in which a conductor is formed by plating. The insulating board and the wiring sub board are horizontally laid out. The insulating layer is laid out to cover a boundary portion between the insulating board and the wiring sub board and continuously extends from the insulating board to the wiring sub board. A resin which constitutes the insulating layer is filled in the boundary portion. The conductor is electrically connected to the wiring layer.