A wiring substrate includes a heat spreader, a first insulating layer provided on the heat spreader via an adhesion layer, the first insulating layer, a plurality of through wirings formed to fill through holes provided at the first insulating layer, respectively, a thermal diffusion wiring provided on the first insulating layer so as to be connected to the through wirings, the thermal diffusion wiring being configured not to be electrically connected to a semiconductor device, an electrical connection wiring provided on the first insulating layer, the electrical connection wiring being configured to be electrically connected to the semiconductor device, wherein the heat spreader is provided with a projection portion, made of a composition same as the heat spreader, at a surface of the heat spreader on which the adhesion layer is formed, the projection portion being aimed at least at an area overlapping the through wirings in a plan view.