A printed wiring board includes a core substrate having a penetrating hole, a first circuit on a first surface of the substrate, a second circuit on a second surface of the substrate, and a through-hole conductor in the hole connecting the first and second circuits. The hole has first and second opening portions. The first opening portion becomes thinner toward the second surface. The second opening portion becomes thinner toward the first surface. The first opening portion has first and second portions. The second opening portion has first and second portions. The first and second portions of the first opening portion form inner walls bending inward at the boundary between the first and second portions. The first and second portions of the second opening portion form inner walls bending inward at the boundary between the first and second portions.