A presumption technique to bound the landslide influence area on a topographic map is presented in this paper. First, three dimensional geometry of underground slide surface is presumed by analyzing the surveyed trajectory of marked points on the landslide area. Next, the intersection of two surfaces, the slide surface and topographic surface, is graphically analyzed. Finally, the boundary line of landslide influence is drawn on the topographic map.The reliability of the boundary line can be examined by the compatibility condition with the landslide phenomena such as cracks, scarps and lateral ridges plotted on the map.Thus the extent of the landslide influence can be presumed to the area where no evident phenomena is discovered. Analytical example applied to Komoro landslide area demonstrates the utility of this technique.