To solve the following problem: in the conventional connection structure of a cavity waveguide and a dielectric waveguide, the length of a through hole provided in a conductor plate can not be made shorter than the length of the inner wall of a cavity waveguide, and the connection structure can not be thereby miniaturized and reduced in weight.

In the connection structure of the dielectric waveguide mounted on the surface of a printed circuit board and the cavity waveguide attached to the back of the printed circuit board, the dielectric waveguide has a slot in which a conductor film is not formed and a dielectric is exposed on a face facing the printed circuit board, the printed circuit board has a via hole at a position facing the slot, the conductor plate is disposed between the printed circuit board and the cavity waveguide, the conductor plate has the through hole at a position facing the slot, and the through hole is formed so as to have an opening in which a width at a center part is narrower than a widths at both ends on the surface of the conductor plate.