A printed circuit board includes: a conductor plate below the inner dielectric layer; some vias through the inner dielectric layer, bonded to the conductor plate, centered at respective points on an upper surface of the conductor plate; a ground conductor above the inner dielectric layer, bonded to the vias, extending outwardly from any quadrangle with vertices being the nearest four points of the points; an electromagnetic resonance plate above the inner dielectric layer and inside the quadrangle, electrically connected to the ground conductor and the vias with a portion other than a protruding outer edge serving as a junction; an upper dielectric layer above the electromagnetic resonance plate; and a differential transmission line pair composed of a pair of strip conductors overlapping with the electromagnetic resonance plate, above the upper dielectric layer. The conductor plate and the vias constitute an electromagnetic field confinement structure.