A circuit board comprises a substrate; a through hole penetrating the substrate along with a direction of a thickness thereof; and a through hole conductor covering an inner wall of the through hole. The substrate comprises a first fiber layer, a second fiber layer, and a resin layer arranged between the first fiber layer and the second fiber layer. Each of the first fiber layer and the second fiber layer has a plurality of fibers and a resin arranged among the plurality of the fibers. The resin layer contains a resin and doesn't contain a fiber. The inner wall of the through hole, in a cross-section view along with the direction of the thickness of the substrate, comprises a curved depression in the resin layer.