We have a lot of organic waste, especially in urban area. Urban cities should manage to treat its organic waste within the cities as much as possible. In order to run composting system of organic waste successfully, we need more green open space where recycled compost can return to the soil. Composting also improves the urban soil, and the improved soil can grow rich and healthy green. This will also be effective in controlling heat-island phenomenon and floods in urban areas. However, there are some risk affecting our environment and health in recycled compost. Therefore, we should structure the recycling system after careful consideration, i.e. we should consider the correspondence between organic waste's risk and space's property. From this point of view, urban green open space can be ranked as Green Open Space for Return, in which recycled compost can return to the soil, more safety. In this study, we try to grasp the area of Green Open Space for Return in Musashino-city, Tokyo, from the data of green covered space. In addition, we examine the possibility and subject for securing necessary space. And consequently, we show that in some chou-chou-moku area, it is possible to return recycled compost, which the population dumped, to the soil by counting not only the public green open space but also private gardens.
