A combustor of a gas turbine engine is fed with liquid ammonia and that liquid ammonia is burned to drive a turbine. Inside the exhaust passage of the gas turbine engine, an NOX selective reduction catalyst is arranged. Inside the intake air which flows into the compressor, liquid ammonia is fed. This liquid ammonia is used to cool the intake air. The NOX which is contained in the exhaust gas is reduced by the unburned ammonia which is exhausted into the exhaust passage by the NOX selective reduction catalyst.