PURPOSE: To simplify the constitution of an antenna device by using an array antenna set opposite to a secondary paraboloidal reflector and a lotman lens which excites said array lens to constitute a primary radiator which excites a radiation system consisting of paraboloidal reflectors sharing a focal point.

CONSTITUTION: A main paraboloidal reflector 1 and a secondary paraboloidal reflector 2 share a focal point F and constitute a radiation system for plane wave/plane wave conversion. An array antenna 3 which excites the reflector 2 with a plane wave against the reflector 2 contains antenna elements 31∼3n which are arrayed within the same plane. These elements 31∼3n are excited by a lotman lens 5. The maximum distance R between the antenna 3 and the reflector 2 is set as R≤2D2/λ when the maximum opening amount of the antenna 3 is set at D. In such a way, it is possible to obtain a beam in the desired direction and to improve the antenna efficiency with a simple constitution of an antenna device.