To improve estimate accuracy of water distribution by correcting demand estimate of water distribution while taking weather data into consideration.

Actual data of rainfall, temperature, humidity, and percentage of sunshine are extracted from an actual data file through an actual data extraction section 23. Estimated data used for demand estimate immediately before water distribution are extracted from an estimate data file 22 through a past estimate data extraction section 24. Percentage of errors between actual data and estimate data of rainfall, temperature, humidity, percentage of bright sunshine is separately calculated by a weather-correction coefficient operation section 25. And correction coefficients are separately extracted from a table corresponding to coefficients in which the percentage of errors is made to correspond to the correction coefficients and the demand estimate of water distribution is corrected on the basis of respective correction coefficients by a demand estimate correction section 26 to obtain corrected demand estimate value.