To provide a 4-port polarization coupler which requires comparatively small mounting space as an antenna mounted on an artificial satellite.

Coupling holes Va and Vb which are connected to the rectilinear parts formed at one of both ends of each of two waveguides 11 and 14 are formed horizontally and opposite to each other on the side face, included in the same section of a waveguide 10 and on the basis of the axis of the waveguide 10. Meanwhile, the coupling holes Ha and Hb which are connected to the rectilinear parts formed at one of both ends of each of two waveguides 12 and 13 are formed vertically and opposite to each other on the side face of the waveguide 10 respectively. The other end of each of both waveguides 11 and 12 are connected to a first power distributor 5, and the other end of each of both waveguides 13 and 14 are connected to second power distributor 6. Then a third power distributor 7 serving as an input part is connected to both the distributors 5 and 6 via the waveguides 15 and 16 respectively.