A center vent tube aligning mechanism which aligns a center vent tube inserted into a hollow shaft is provided with: an annular portion which is coaxially provided with the center vent tube in an outer side of the center vent tube in a radial direction thereof; a flexible portion which protrudes in a direction along an axis of the center vent tube from the annular portion; an abutting portion which is connected to the flexible portion and which abuts an inner circumferential surface of the shaft; and a cylindrical sleeve which surrounds the center vent tube from the outer side in a radial direction of the center vent tube and which is supported by a reaction force that the abutting portion receives from the inner circumferential surface of the shaft.