A ventilation flow path, a cooling air flow path, a mixing space, and a mixed air flow path are formed in a gas turbine rotor. The ventilation flow path guides compressed air farther on an axially upstream side than an air discharge port of a compressor to an interior of a compressor rotor as compressor extracted air. The cooling air flow path guides cooling air to a part farther on an axially downstream side than the air discharge port. The compressor extracted air and the cooling air are mixed in the mixing space. The mixed air flow path guides mixed air containing the compressor extracted air and the cooling air into a turbine rotor.