PURPOSE: To prevent noxious odor pollution at a low construction cost by removing odor by passage of exhaust gas through an artificial soil covered on the top of the sewage treatment tank.

CONSTITUTION: A plurality of exhaust holes are made on the top bed of a sewage treatment tank. Exhaust pipes are arrange on the top thereof while perforated exhaust pipes 10 mounted on the upper side wall thereof. Then, an artificial soil 11 having a glomerate grain structure is covered around these exhaust pipes to remove and decompose components of noxious odor in the exhaust gas.