NOVELTY - An apparatus is provided with an ammonia-removal unit which removes ammonia in the digestive liquid derived from a methane fermentation-treatment unit which methaneferments a nitrogen-containing organic wastewater, and aeration unit (16) for maintaining the digestive liquid in the processing tank at aerobic conditions. The digestive liquid inflow path (12) of digestive liquid derived from the methane-fermentation treatment unit flowing into the processing tank, and ammonia removal processing water-flow appearance path (14).    USE - Apparatus is used for treating wastewater e.g. livestock farming wastewater like livestock excrement, foodstuff wastewater and sludge supernatent liquor.    ADVANTAGE - The method efficiently enables the wastewater treatment method using the apparatus.    DETAILED DESCRIPTION - An apparatus is provided with an ammonia-removal unit which removes ammonia in the digestive liquid derived from a methane fermentation-treatment unit which methaneferments a nitrogen-containing organic wastewater, and aeration unit for maintaining the digestive liquid in the processing tank at aerobic conditions. The digestive liquid inflow path of digestive liquid derived from the methane-fermentation treatment unit flowing into the processing tank, and ammonia removal processing water-flow appearance path in which the ammonia removal processing water which performs the ammonia removal processing, is made to flow out of processing tank. The gas lead-out passage (17) which extracts the gas emitted within the processing tank out of processing tank, is provided in the digestive liquid in the processing tank. The ammonia is converted in the digestive liquid into nitrogen gas. The organic acid assimilation microbe consumes the organic acid in the digestive liquid. The ammonia-removal unit is processing tank. An INDEPENDENT CLAIM is included for wastewater treatment method.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of wastewater treatment apparatus.    Digestive liquid inflow path (12)    Ammonia removal processing tank (13)    Ammonia removal processing water-flow appearance path (14)    Aeration unit (16)    Gas lead-out passage (17)