In this paper, the writer examined some factors exerting influence on the measurement of underground temperature and controlling the underground temperature. As the results of this examination, next factors were clarified. a) On the factors exerting influence on the measurement of underground temperature: 1) Inflow of the air into opened hole and the heat of friction between iron bar and wall of hole had no effect on the measurement of underground temperature. 2) Inserted thermometer into the hole was read the temperature after five minutes ago. 3) Diurnal variation of underground temperature at one meter in depth was not in existence against a wide range of thermal diffusivity of the landslide soil mass. 4) Thermal diffusivity of tuff in the Matsunoyama landslide area was 0.002-0.012cm2/sec., and unchangeable layer of underground temperature is about 60 centi-meters in depth. 5) Surface water around the measurement points had no effect on the underground temperature at one meter in depth, but underground water exuding from the wall of hole had an effect on it. b) On the factors controlling the underground temperature: 1) The distributed pattern of underground temperature was not controlled by geological and topographical factors in and around a landslide area. 2) The distributed pattern of underground temperature was controlled by ground surface condition, a forest and a rice field had a large effect on the underground temperature at one meter in depth. Accordingly, each measured value should be corrected in obedience to each ground surface condition of the measurement point. 3) Vein-stream of underground water had a large effect on the underground temperature at one meter in depth. In the case of the Matsunoyama landslide area, the vein-stream of underground water had the dimension of 10 or 30 meters radius, and this value did not change so large against the variation of season.