PURPOSE: To automatically control the cooling speed of quickly balancing the temperature of a cooled position by placing a field winding within a cylindrical support member supported in a rotating axis and providing a cavity through which a gas coolant flows and also a storage tank for a coolant from the external to adjust the value travel of a solenoid valve in accordance with the output of plural temperature detectors in each position and supply the coolant.

CONSTITUTION: Cylindrical support members 8, 9 are rotatably supported by rotation axes. Cavities 14, 15 allowing a gas coolant to flow along the surface of a wall, a winding accommodation part for accommodating a field winding 1 and a coolant storage tank 5 for cooling a field winding are provided by the support members 8, 9. The storage tank 5 is supplied with a coolant from the external through a cavity 16. Only a coolant to have already been used is discharged from exhaust tubes 31, 32 to the external. Temperature detectors 2 to 4, 10 to 12 are arranged in each cooled position to input the detected results into a controller 100. The controller 100 adjusts the opening degree of solenoid valves 17 to 19, thereby controlling the flow rate of the coolant in accordance with the output of each temperature detector. Thereby, the temperature of each cooled position is quickly balanced.