PURPOSE: To clean a cooling air-passage with a less labor in a short time by inserting a high-pressure flexible hose into a cooling air-passage inside a gas turbine rotor while transmitting vibrational force thereto, for injecting compressed gas to a passage wall from the hose while being allowed to make sulsation.

CONSTITUTION: A gas turbine is provided with a cooling air-passage 18 in a rotor disk 8 for forming a turbine rotor. In this case, a movable ring 9 provided with a hollow passage 16 is removed from the rotor disk 8 when the cooling air-passage 18 is cleaned. At the same time, a movable wing cooling air introduction line 22 and a labyrinth seal 21 on a casing 21 are removed. Next, a high- pressure flexible hose is inserted into the inlet part 20 and the connecting hole part 23 of the cooling air-passage 18 while transmitting vibrational force from the sheath part of the casing 19. Sequentially, compressed gas is introduced from the high-pressure flexible hose, and it is injected to the cooling passage wall while being allowed to make pulsation, moreover it is conveyed to the outside by crashing fouling materials on the passage.