A radio wave receiving converter is provided with a circular waveguide unit to which a vertically-polarized wave and a horizontally-polarized wave are input, first and second board holding units provided on the upside and the downside of the circular waveguide unit and holding first and second circuit boards, respectively, and first and second feed probes having tip portions provided to protrude into a waveguide element in parallel with the vertically-polarized wave and the horizontally-polarized wave, respectively, and having proximal end portions connected to the first and second circuit boards, respectively. Accordingly, the first and second board holding units are provided on the upside and the downside of the circular waveguide unit, and thus there is no need to use a sliding insert in the design of a die, so that the die can easily be fabricated at low cost.