A printed wiring board includes a substrate having a first surface, a second surface on the opposite side of the first surface and a through-hole extending between the first and second surfaces, a first conductive circuit formed on the first surface of the substrate, a second conductive circuit formed on the second surface of the substrate, and a through-hole conductor filling the through-hole and connecting the first and second conductive circuits. The through-hole has a first opening portion tapering from the first surface toward the second surface and a second opening portion tapering from the second surface toward the first surface. The substrate is made of a resin and a reinforcing material portion in the resin. The reinforcing material portion has a protruding portion protruding into the through-hole at the intersection of the first and second opening portions. The protruding portion encroaches into the through-hole conductor.