A lens antenna having high antenna efficiency, low sidelobe levels, and that is easily assembled. The lens antenna includes a first horn made of a metallic conductor, a second horn made of a high-frequency absorbing plastic material, and a lens for controlling the power distribution at an aperature of the horn. Screws may be used to assemble the first horn, the second horn, and the lens. Though some of the microwave signals input through the circular waveguide of the first horn are reflected on the surface of the lens, most of the microwave signals are absorbed by the second horn. Moreover, because no wave absorber is bonded to an inner wall of a conical horn, nothing screens the microwave signal, the power density distribution at the aperture of the lens is not disrupted. Therefore, it is possible to obtain a desired power density distribution.