To improve ignitability by adopting a firing gaseous fuel into the combustor a gas turbine engine using liquid fuel via a spark plug.
When a spark plug 2 operates after receiving a start command out of an engine controller 1, a gas fuel feed valve 3 is opened and gas fuel in a gas fuel cylinder 4 is fed to the inside of a combustor 7 by way of an orifice 5, a line filter 6 and the spark plug 2 and ignited. At this time, after ignition is ascertained by a temperature sensor 13, the opening of a liquid fuel flow regulating valve 8 is controlled by the engine controller 1 and liquid fuel in a liquid fuel tank 9 is boosted by a fuel pump 10. Then the liquid fuel is injected into the combustor 7 from a fuel nozzle 11 and ignited, and at a point of time when sufficient acceleration is secured, the gas fuel feed valve 3 is closed by the engine controller 1, and any operation of the spark plug is stopped, thereby shifting to the combustion of the liquid fuel alone.