This study aims to explain the effect of land use and local insolation environment on surrounding air temperature in mountain area. In summer of 2008, we measured the thermal environment in Fukutomi town surrounded by mountains. The insolation environment was estimated by GIS based on the sun orbit. As a result, we confirmed the difference of air temperature variation both in the morning and evening because of the difference of insolation environment in each measurement point around. In addition, we found that not only land use but also diurnal insolation environment affects the air temperature at night.