Detection of the spatial scale of heavy precipitation is important for the prevention of disasters. This study analyzed the spatial scale of heavy precipitation based on observed data at the railway observational stations and the meteorological stations in Kanto Plain. The results can be summarized as follows: The simultaneous occurrence area of precipitation becomes smaller when the criterion of precipitation and/or the distance increases. Heavy precipitation exceeding 30mm (130mm) during 1-hour (24-hour) occurs simultaneously within the distance of about 4km (>30km) at the probability of 0.5. The spatial scale of heavy precipitation is larger in case of typhoon rather than front, low, and thunderstorm. The simultaneous occurrence area of precipitation seems to have southwest-northeast oriented long axis. Moreover, the spatial scale of heavy precipitation is larger in southeastern part rather than in northwestern part of Kanto Plain.