A gas turbine, in which, in operation, combustion gas generated by supplying fuel to a combustor where the fuel is combusted with compressed air compressed at a compressor is supplied to a turbine to acquire rotational power, the gas turbine comprising: a plurality of stator blades and rotor blades that are alternately disposed in a turbine cylinder of the turbine; pressurizing means connected to a branching channel branching from a discharge-side channel of the compressor and capable of carrying out an operation for introducing and pressurizing a heating medium independently from the compressor by means of a motor for driving the pressurizing means; a heating-medium supply channel arranged to guide pressurized heating medium pressurized at the pressuring means to a turbine-cooling-medium channel (50,31a) which is provided in a stationary component of the turbine and which is a channel connecting the turbine cylinder, the stator blades and a blade ring of the turbine and which is used for temperature control by cooling and heating, wherein the blade ring is a member attached to the turbine cylinder in such a manner that it surrounds the outer circumference of the rotor blades; and a heating-medium return channel arranged to guide the pressurized heating medium that has passed through the turbine-cooling-medium channel (50,31a) to the discharge-side channel such that the flows are combined, wherein the pressurizing means is arranged to be operated at startup of the gas turbine and in preparation immediately before startup to raise the temperature by letting the pressurized heating medium flow in the turbine-cooling-medium channel (50,31a), and is configured to adjust pressure and amount of the pressurized heating medium by operation control of the pressurizing means. a plurality of stator blades and rotor blades that are alternately disposed in a turbine cylinder of the turbine; pressurizing means connected to a branching channel branching from a discharge-side channel of the compressor and capable of carrying out an operation for introducing and pressurizing a heating medium independently from the compressor by means of a motor for driving the pressurizing means; a heating-medium supply channel arranged to guide pressurized heating medium pressurized at the pressuring means to a turbine-cooling-medium channel (50,31a) which is provided in a stationary component of the turbine and which is a channel connecting the turbine cylinder, the stator blades and a blade ring of the turbine and which is used for temperature control by cooling and heating, wherein the blade ring is a member attached to the turbine cylinder in such a manner that it surrounds the outer circumference of the rotor blades; and a heating-medium return channel arranged to guide the pressurized heating medium that has passed through the turbine-cooling-medium channel (50,31a) to the discharge-side channel such that the flows are combined, wherein the pressurizing means is arranged to be operated at startup of the gas turbine and in preparation immediately before startup to raise the temperature by letting the pressurized heating medium flow in the turbine-cooling-medium channel (50,31a), and is configured to adjust pressure and amount of the pressurized heating medium by operation control of the pressurizing means.