The waveguide device, in which first/second openings are formed at end parts of a waveguide path, comprises a waveguide path obtained by uniting first/second waveguides. The first waveguide is provided with a first recessed part which has an opening with a same shape as the first opening and has a bottom part formed in a first direction as seen from the opening. The second waveguide is provided with a second recessed part which has an opening with a same shape as the second opening and has a bottom part formed in a second direction as seen from the opening. The first/second waveguides are united in a manner such that, positions of the bottom parts of the first/second recessed parts are different from each other in a direction differing from the first/second directions, and the first/second recessed parts connect with each other at the respective bottom parts.