PURPOSE: To prevent the generation of fretting only by adding a simple path, by taking-out a portion of the pressurized medium from the discharge side of an auxiliary machine in operation and efficiently introducing said medium into the impeller of the auxiliary machine in operation stoppage and always revolving the auxiliary machine compulsorily at low speed.

CONSTITUTION: A motor 1 is arranged onto a motor base 5, as an auxiliary machine during operation stoppage, and an impeller 2 is installed at the top edge of the shaft of the motor and revolved in the casing 3 of the auxiliary machine. The pressurized medium supplied from the discharge side of the auxiliary machine in operation is jetted-out from an air introducing pipe 6 in the vicinity of the upper part of the casing 3. In this case, the top edge of the air introducing pipe 6 is formed into nozzle form, and the center part of the above-described impeller 2 forms an angle of 30W45° with respect to the tangential line of the impeller 2 and permits the medium to be jetted-out in the direction of normal revolution. Therefore, since the auxiliary machine in operation stoppage always revolves at a low speed, the generation of fretting is prevented, and the operation efficiency can be improved.