Work function of low index crystal facet of tungsten was evaluated by measuring field emission characteristics using a probe hole system. Unlike the conventional method, the authors derived the work function through the analysis of the relationship between the slope and intercept of the Fowler-Nordheim plot, which we call the Seppen-Katamuki analysis. Measurements were done in a vacuum vessel which was evacuated down to approximately 10(-7) Pa. The etched tungsten emitter was heated to have hemispherical apex with the radius of 110 or 220 nm. The field emission was caused by an applied voltage between the emitter and a fluorescent screen. The screen has a small aperture with a diameter of 2 mm as a probe hole. Behind the screen, the authors placed a transparent collector. The authors measured the field emission characteristics originating from (0 11), (111), (121), and (112) facets through the probe hole, for six times for each facet. The obtained characteristics were examined in a two-dimensional diagram of which abscissa and ordinate are the intercept and slope of the Fowler-Nordheirn plot. The measured characteristics for each facet distributed along a straight line in the chart, and from the slope of the line, the authors derived the relative work function value. The obtained values agreed well with the values shown in the literature. (c) 2007 American Vacuum Society.