An antenna device including: a reflector antenna including a primary radiator, a feed waveguide for feeding radio waves to the primary radiator, and a reflector; and a radome that covers the reflector antenna, in which the antenna device further includes a sidelobe reduction member attached to a vicinity of the primary radiator or the feed waveguide, the sidelobe reduction member reducing a sidelobe in a specific direction of an antenna by at least one of scattering and absorbing of radio waves reflected by the radome out of the radio waves radiated from the reflector antenna. Therefore, it is possible to reduce a sidelobe deterioration caused by reflection waves from the radome.