An antenna device comprising: a first beamforming circuit for forming a radio wave including two polarized waves orthogonal to each other in a first frequency band to output the radio wave in the first frequency band; a second beamforming circuit for receiving the radio wave in the first frequency band output from the first beamforming circuit to output the radio wave in the first frequency band, and for forming a radio wave including two polarized waves orthogonal to each other in a second frequency band to output the radio wave in the second frequency band; and a plurality of primary radiators (7-1 to 7-M) for emitting a beam in the first frequency band in response to the radio wave in the first frequency band output from the second beamforming circuit, and emitting a beam in the second frequency band in response to the radio wave in the second frequency band output from the second beamforming circuit, wherein each of the plurality of primary radiators comprises a horn antenna including a coaxial cylindrical waveguide (7a, 7b), and the plurality of horn antennas are connected to the second beamforming circuit, and the second beamforming circuit is connected to the first beamforming circuit, wherein the second beamforming circuit includes a plurality of coaxial waveguides (21a, 21b) connected to a corresponding one of the plurality of horn antennas, the plurality of coaxial waveguides each include an inner waveguide having one end connected to an inner waveguide of a corresponding one of the plurality of horn antennas, and each inner waveguide of the plurality of coaxial waveguides includes another end connected to the first beamforming circuit, and the plurality of coaxial waveguides each include an outer waveguide having one end connected to an outer waveguide of a corresponding one of the plurality of horn antennas, and each outer waveguide of the plurality of coaxial waveguides includes another end terminated, characterized in that the second beamforming circuit includes a plurality of connecting waveguides connecting among the plurality of coaxial waveguides, and power supply waveguides (23, 24) connected to one coaxial waveguide of the plurality of coaxial waveguides, the power supply waveguides (23, 24) being for providing two polarized waves orthogonal to each other to the one coaxial waveguide. a first beamforming circuit for forming a radio wave including two polarized waves orthogonal to each other in a first frequency band to output the radio wave in the first frequency band; a second beamforming circuit for receiving the radio wave in the first frequency band output from the first beamforming circuit to output the radio wave in the first frequency band, and for forming a radio wave including two polarized waves orthogonal to each other in a second frequency band to output the radio wave in the second frequency band; and a plurality of primary radiators (7-1 to 7-M) for emitting a beam in the first frequency band in response to the radio wave in the first frequency band output from the second beamforming circuit, and emitting a beam in the second frequency band in response to the radio wave in the second frequency band output from the second beamforming circuit, wherein each of the plurality of primary radiators comprises a horn antenna including a coaxial cylindrical waveguide (7a, 7b), and the plurality of horn antennas are connected to the second beamforming circuit, and the second beamforming circuit is connected to the first beamforming circuit, wherein the second beamforming circuit includes a plurality of coaxial waveguides (21a, 21b) connected to a corresponding one of the plurality of horn antennas, the plurality of coaxial waveguides each include an inner waveguide having one end connected to an inner waveguide of a corresponding one of the plurality of horn antennas, and each inner waveguide of the plurality of coaxial waveguides includes another end connected to the first beamforming circuit, and the plurality of coaxial waveguides each include an outer waveguide having one end connected to an outer waveguide of a corresponding one of the plurality of horn antennas, and each outer waveguide of the plurality of coaxial waveguides includes another end terminated, characterized in that the second beamforming circuit includes a plurality of connecting waveguides connecting among the plurality of coaxial waveguides, and power supply waveguides (23, 24) connected to one coaxial waveguide of the plurality of coaxial waveguides, the power supply waveguides (23, 24) being for providing two polarized waves orthogonal to each other to the one coaxial waveguide.