PURPOSE: To obtain a primary radiator to be shared with circularly polarized waves(CPWs) and linearly polarized waves(LPWs) (horizontal/vertical PWs) which can receive both radiowaves of CPWs and LPWs from a satellite using both CPWs and LPWs.

CONSTITUTION: The 1st phase circuit (metallic blocks 3, 4), the 2nd rotary phase circuit (dielectric plate 7) and a square waveguide 9 are successively arranged in the direction from the aperture part (1) side of a circlar waveguide 2 to its terminal end face 5. In the case of receiving a CPW, the CPW is converted into an LPW by the 1st phase circuit, the plate 7 is directed so that the phases of two polarized components in the LPW are not made different and a signal is outputted from the waveguide 9. In the case of receiving an LPW, a phase difference between two polarized components in the LPW which is generated by the 1st phase circuit is eliminated so as to be inphase by rotating the plate 7 and one signal in the LPW is outputted from the waveguide 9, while rotating the plate 7 so that the phase difference is about 180° and outputting the other signal in the LPW from the waveguide 9. The exchanged arrangement of the 1st and 2nd phase circuits is also an available constitution.