A low-energy electron diffraction examination of the ZrO/W(100) surface? which has a remarkably low work function and is practically applied to athermal-field emission cathode for an electron microscope, showed a peculiar pattern. Assuming that reduction of the work function should occur due to a dipole effect of the Zr-O pair at the surface, I-V (intensity versus voltage) analysis was done for the pattern. It is revealed that no model, for which a perpendicular dipole effect on the surface can be expected, gives a small enough R factor to conclude that the model exhibits a real atomic arrangement. The results suggest that it is necessary to consider the parallel dipole effect on the surface.