To provide an ammonia removing apparatus, which can reduce an energy cost with a low-cost equipment and particularly enables a long-term stable operation in a system with a component causative of scaling, such as solids, mixed therein, and to provide an apparatus and a method for treating an organic waste using the ammonia removing apparatus.

The apparatus comprises: a distillation column that brings an ammonical nitrogen-containing organic waste into contact with a steam and separates the ammonical nitrogen from the organic waste to give a treated liquid; a first heat exchanger that heat exchanges the organic waste, immediately before supply into the distillation column, with the treated liquid discharged from the bottom part of the distillation column; a second heat exchanger that heat exchanges an ammonical nitrogen-containing steam, discharged from the upper part of the distillation column, with an externally introduced external water to bring the external water to an internal steam, a drum that, before the introduction of the external steam into the bottom of the distillation column, allows a condensate liquid to flow back into the distillation column; and a steam ejector that performs suction mixing of the internal steam into the external steam.