In a typical urban area with a mixture of old and newly developed areas, the actual situation of drainage from building roofs to roads directly was shown, and the reasons were discussed. In area that direct drainage from building roofs to roads were observed and flooding is predicted by hazard map, the distribution on apartment buildings with an excavated ground floor is shown. Also, the inflow volume into an apartment building in the flooding event was estimated. Based on the results, improvement measures to control flooding in order to make the town safe against flooding were proposed.