The ZrO/W(100) surface has remarkably low work function, and shows a peculiar c(4X2) low-energy electron diffraction (LEED) pattern. The I-V (intensity versus voltage) method is adopted to analyze the LEED pattern as widely used. The direction of Zr-O dipole has been expected vertical to the surface, because the vertical dipole most effectively reduces the surface potential. However, the analysis says that atomic arrangement including only the vertical dipole is not good enough for getting the highly reliable I-V curve, thus, horizontal dipole must be considered.