A wiring board including a built-in semiconductor element includes the semiconductor element, a peripheral insulating layer covering an outer peripheral side surface of the semiconductor element, an upper surface-side wiring provided on an upper surface side of the wiring board, and a lower surface-side wiring provided on a lower surface side of the wiring board. The semiconductor element includes a first wiring structure layer including a first wiring and a first insulating layer alternately provided on a semiconductor substrate, and a second wiring structure layer including a second wiring and a second insulating layer alternately provided on the first wiring structure layer. The upper surface-side wiring includes a wiring electrically connected to the first wiring via the second wiring. The second wiring is thicker than the first wiring and thinner than the upper surface-side wiring. The second insulating layer is formed of a resin material and is thicker than the first insulating layer.