PURPOSE: To promote the propagation of microorganisms and to solidify sludge as well as to clean the org. matter in sewage by disposing an oyster shell packed tank, fishing net scrap packed tank, and brick scrap packed tank into a separating tank thereby constituting the living waste water cleaning device.

CONSTITUTION: Bulkheads 5 for partition are erected at prescribed intervals in an existing water channel 4, such as flume or small river, which is already finished with concrete or the like and the seven separating tanks are installed like a staircase. The grit tank 6, the oyster shell packed tank 1, the water grass tank 7, the fishing net scrap packed tank 2, the water grass tank 7, the brick scrap packed tank 3, and the inspection tank 8 which is disposed at the terminal and in which fishes are released, are disposed in this order from above. The effect of decomposing and cleaning the org. matter in the sewage by the microorganisms is vigorous in the respective filter media packed tanks and the nitrogen and phosphorus components are absorbed as the nutrients of the water grass, by which the BOD and COD in the sewage are removed by about 85%.