To solve a problem that, in a conventional structure, a part of electromagnetic waves radiated from a primary radiator is reflected by a sub-reflector and is again directed to the primary radiator, resulting on degradation of VSWR characteristics of an antenna.

A body of a sub-reflector 2 is molded integrally with a radome 5 with a resin, a hyperboloid for reflecting electromagnetic waves is provided on an inner surface of the radome 5 as the sub-reflector of a Cassegrain antenna, and the hyperboloid is conductively plated to structure the sub-reflector 2. At this juncture, a non-conductor part 4 which is not practically plated is provided at an apex of the hyperboloid of the sub-reflector 2.