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Urban development causes serious changes to watershed conditions by decreasing storage area, introducing pavement and channeling. As a result, the peak discharge has been increasing and the arrival time of peak becomes shorter. The purpose of this study is to estimate the change of flood discharge by transition of landuse in the Mikasa River watershed with the effect of the existing storage facilities such an irrigation ponds. To estimate that we applied the distributed runoff model considering the landuse in 1900, 1950, 1976 and 1997 of the Mikasa River watershed about flood disaster in July 19, 2003. The result of calculation showed that the peak discharge at Sanno Bridge has been increased 27% for the last 100 years result from transition of landuse in the Mikasa River watershed.