NOVELTY - A wastewater treating device, comprises a raw wastewater equalization tank, first anaerobic/anoxic tank, oxic tanks, sedimentation tank, and sludge return pump.    USE - For refining tannery wastewater having much nitrogen content, significant change of load and a great amount of harmful matters like heavy metals; and reduction of its sludge.    ADVANTAGE - The invention treats a great amount of wastewater in a short time, suitable for a huge amount of industrial waste water. It enables anoxic digestion and denitrification to occur in a single reactor, which reduces the area of site but enhances the treating efficiency of organic high-density poisonous wastewater. The activated sludge sent back to a first anaerobic/anoxic tank and decomposed by the anoxic digestion used as the source of carbon easily lacking in denitrification and thus need no external supply of carbon. The supernatant of the precipitation is sent back to the first anaerobic/anoxic tank and mixed with the incoming raw wastewater so that the nitrate not perfectly removed in the second anoxic tank is eliminated through denitrification.    DETAILED DESCRIPTION - A wastewater treating device for tannery waste water and for sludge reduction, comprises a raw wastewater equalization tank (110) for storing raw wastewater. A first anaerobic/anoxic tank (120) causes the wastewater coming from the equalization tank to continuously undergo anoxic digestion and denitrification. A septum (210) divides the inside of the first anaerobic/anoxic tank while installed movably up and down so that the divided parts communicate with each other. A sludge drain valve (220) removes the activated sludge in the first anaerobic/anoxic tank. Oxic tanks (130, 140) continuously incubates the mixed group of microbes in the condition of oxygen by means of various organic matters of waste water coming from the first anaerobic/anoxic tank as nutrient media, includes a blower (132) and a refuser (132a) for pumping to the tanks. A second anoxic tank (150) continuously incubates the mixed group of microbes in an anoxic condition, taking as the nutrient media various organic matters of the organic matters of the waste water coming from the second oxic tank. A sedimentation tank (160) precipitates the activated sludge coming from the second anoxic tank. A sludge return pump (240) for sending back the activated sludge sunk in the sedimentation tank to the first anaerobic/anoxic tank and first oxic tank. A supernatant return pump (250) sends back part of the supernatant of the sedimentation tank to the first anaerobic/anoxic tank, mixing it with the incoming raw wastewater.    DESCRIPTION OF DRAWING(S) - The figure shows a construction diagram of the device.    Raw waste water equalization tank (110)    Agitator (114)    First anaerobic/anoxic tank (120)    Oxic tanks (130, 140)    Blower (132)    Refuser (132a)    pH controller (134)    pH control tank (134a)    Driving pump (134b)    Second anoxic tank (150)    Sedimentation tank (160)    Drain tank (170)    Septum (210)    Sludge drain valve (220)    Scraper (230)    Sludge return pump (240)    Supernatant return pump (250)