In this study, a new automated construction method of minute road segments is developed. Numerical simulation models for rainfall-runoff and flood inundation model considering process on roads were based on so-called “Minute road segments” that are formed as simple shape polygons to calculate the flow on roads. In the developed method, firstly crossroads are demarcated from road sections of uninterrupted flow in order to simplify a polygon of road. Secondly road sections and crossroads are divided into minute road segments. The developed method was applied for Kanda catchment and the shapes of minute road segments were validated.It was demonstrated that minute road segments can be created by using the method of this study.