In order to obtain knowledge of the effects of air temperature, precipitation, and solar radiation to river water temperature of different timescales, statistical analyses were conducted using the meteorological and river water temperature data of 10 years. Two types of data set were used; one was 82 sampling points of 27 rivers where data were obtained monthly, and the other was the 5 sampling points of different rivers where data were obtained daily. The variations of the river water temperature on the variations of air temperature of daily scale were estimated to 0.1-0.5 (°C/°C) and were also influenced by the hydrological scale of river basin. The variations in yearly scale were estimated to 0.5-1.5 (°C/°C). The variations in summer were bigger than those of other seasons, suggesting the effects of solar radiation. Assuming that solar radiation was constant, the variation of yearly scale was estimated to about 0.5-0.85(°C/°C). Under similar assumption, the long term variation was estimated to about 0.84-0.89(°C/°C).