This paper introduce the two types of submillimeter-wave horn antennae designed by the authors and present the experimental results obtained by an evaluative testing system that has also been developed by the authors. Submillimeter-wave components are widely used in radio-astronomical observation apparatuses. It should be noted, however, that, because the submillimeter-waves radiating from astronomical objects are extremely weak, there is a need to minimize (1) the various losses possibly occurred in the wave-receiving unit of observation apparatus, and (2) the quantity of the unwanted electromagnetic waves mixing in. With a view to achieving this objective, therefore, the authors provide in this paper their theoretical and experimental analyses of the submillimeter-wave horn antenna as well. It is a well-known fact that a corrugated horn antenna possesses very low levels of cross-polarized field intensity and high levels of radiation gain. It is for this reason that the authors have chosen to use corrugated horn antennae or, to be more specific, two types of such antennae -- one designed by the authors for use in the range of 280 GHz to 360 GHz frequencies and tested actually to ascertain its characteristics, and the other designed for use in the range of 385 GHz to 500 GHz frequencies and tested actually to ascertain its characteristics. Note that (1) the measurements of the antenna beam patterns have been found to largely correspond to those of the numerical analyses, (2) it may therefore, be safely assumed that the corrugated horn antennae presented here are functionally as efficient as they were designed, and (3) it may well be concluded that the measuring system developed by authors for evaluating submillimeter-wave horn antennae doubtless serves its useful purposes.