The present invention relates to an aeration tank for organic wastewater and an aeration processing device using the aeration tank. The objects of the present invention are to: increase the purification efficiency of the aeration processing device for livestock wastewater, and so on, reduce the cost of facilities, and thereby prevent the environmental pollution. The solving means is to provide an aeration tank for organic wastewater, which comprises an external tank 1 and an aeration pipe 2 installed inside the external tank. This aeration pipe 2 is configured with inlets 3 at the lower portion of the pipe wall and distributor holes 4 at the upper portion of the pipe wall. Inside the lower portion of the aeration pipe, a diffuser 6 is attached to an air flow pipe 5. The processed water decomposed by organisms inside the external tank 1 is aerated in the aeration pipe 2. From a part of distributor holes, the processed water and the generated foam simultaneously distribute and revive the adherent organisms inside the external tank 1, as well as transport the adherent organisms to a sludge settling tank. In the present invention, a plurality of such aeration tanks are installed to obtain purified water, by sequentially aerating, circulating and purifying the clear water above the foam, which has been transported from the initial aeration tank to the sludge settling tank, in the remaining aeration tanks. The purified water is used as the cleaning water of livestock farms and the fertilization water.