The horn array antenna includes a horn (10), a first polarization guide (30), and a second polarization guide (50). The horn (10) guides inputting and outputting radio waves, and includes a inclined section (15) tapered along a propagation direction of a radio wave and having an internal aperture formed at one end having a narrower width and at least one of ledges (17) projected at the end toward an inside of the internal aperture. The first polarization guide (30) is connected to the horn (10) and guides a first polarization. The second polarization guide (50) is connected to the horn (10), disposed in parallel with the first polarization guide (30), and guides a second polarization having directivity perpendicular to the first polarization.