To further increase a purifying function for org. waste water by utilizing characteristics of charcoal.

In the device, a char tank 6 for adsorbing heavy metal, a low temp. carbonized char tank 3, a high temp. carbonized char tank 4 and a mixed char tank 5 are disposed in order from the upstream side of natural river 1 toward downstream side. Each char tank is formed by dividing both upstream and downstream sides with partitions 7 and 7 and packing the chars carbonized at a prescribed carbonizing temp. A low temp. carbonized char layer 32 is formed with the char 31 carbonized at 400-700°C and having pH of 6-8, a high temp. carbonized char layer 42 is formed with the char 41 carbonized at 700-900°C and having pH of ≥8, a mixed char layer 52 is formed by mixing the char 31 and the char 41 and a char layer 2 for adsorbing the heavy metal is formed with the char carbonized at 900-1200°C. The low temp. carbonized char layer becomes a proliferation zone of fungi and protozoans and the high temp. carbonized char layer becomes a proliferation zone of waterweed and a same phased biological purifying process as the self-purifying function inherent in a river is realized.