To provide an ammonia removing installation with a catalyst combustor less in working power, compact and easy to maintain.

The ammonia removing installation comprises an ammonia dispersing tower 3 for introducing dewatered filtrate containing ammonia and putting it in contact with steam supplied from a boiler to gasify the ammonia and the catalyst combustor 8A for introducing the gasified ammonia and oxidizing it in a catalyst layer with air to convert it into nitrogen. The catalyst combustor 8A has a combustible gas supply nozzle 82 and a temperature detecting means 9. By adjusting a combustible gas adjuster valve 7 depending on a temperature detected by the temperature detecting means 9, the flow rate of combustible gas to be introduced is controlled to hold the catalyst layer at a preset temperature.