Provided is an ammonia detoxification device that, when detoxifying ammonia by thermal decomposition, is capable of preventing the generation of nitrogen oxides. That is, the problem is solved by configuring the ammonia detoxification device using: an electric heater; an ammonia decomposition chamber that accepts an ammonia-containing gas to be treated and thermally decomposes the ammonia in the absence of oxygen using heat from the electric heater; a thermally decomposed gas-burning chamber that accepts the nitrogen- and hydrogen-containing gas to be treated that has been generated by the thermal decomposition of the ammonia and discharged from the ammonia decomposition chamber, and an air-supplying means for supplying air from the outside into the thermally the thermally decomposed gas-burning chamber to burn the hydrogen.