A gas turbine engine includes: an air flow control system installed in an air intake path for introducing air to a compressor. The air intake path is located outside and upstream with respect to the compressor. The engine also includes intake air flow control means for controlling an intake air flow by operating the air flow control system according to a load of the engine so as to maintain an air-to-fuel ratio in the combustor within a proper range suited to suppress a discharge of an atmospheric pollutant.