The disclosure provides an antenna device (1), which includes a waveguide antenna (20) having wall surfaces and for emitting a radio wave in a direction substantially perpendicular to an emission face that is one of wall surfaces of the waveguide antenna extending in an elongated direction of the waveguide antenna, a plate-shape two-dimensional opening slots for beam formation formed in the waveguide antenna on the emission face side, a power feed waveguide module (30, 50) arranged in the rear face of the waveguide antenna opposite from the emission face and for supplying electric power to the waveguide antenna, and a cylindrical radome (10) having a substantially circular cross-section of a diameter that is substantially equal to a length of the emission face in a direction perpendicular to the long-side direction so that the waveguide antenna is contained in the radome so as to be arranged at substantially the centre of the radome.