Diurnal variations of surface wind speeds during fair weather in the summer were revealed in central Japan, including data at Automated Meteorological Data Acquisition System (AMeDAS) and mountain station data above 2000 m above the mean sea level (a.s.l.) archived by an inter-university cooperative project, in relation to the altitude and concave-convex conditions around each station. AMeDAS stations belonging to Japan Meteorological Agency (JMA) are located below 1500 m, and most of them were categorized as being in concave topography with stronger daytime wind speed anomalies than in nighttime. At stations above 2000 m a.s.l. operated by each university, wind speed anomalies at night were stronger than those during the day except at the station without convex topography within a 1-5 km scale. Nocturnal enhancement of wind speeds at representative mountaintop stations appeared with prevailing Pacific Highs in synoptic pressure patterns, but it did not always appear in the same day and the absolute nocturnal wind speed varied day by day. The degree of concavity was not clearly related to the wind speed anomaly, and the degree of convexity was linearly related to the wind speed anomaly at a scale of approximately 10 km.