A center vent tube aligning mechanism for a jet engine, adapted to align a center vent tube inserted into a hollow shaft, the center vent tube aligning mechanism comprising: - an annular portion adapted to be coaxially provided with the center vent tube in an outer side of the center vent tube in a radial direction thereof; - a flexible portion protruding downstream from an edge portion of the annular portion in an outer side in the radial direction thereof; - an abutting portion connected to the flexible portion, and adapted to abut an inner circumferential surface of the shaft; - a cylindrical sleeve integrated with the annular portion at an upstream end of the cylindrical sleeve, adapted to surround the center vent tube from the outer side in the radial direction of the center vent tube, and adapted to be supported by a reaction force that the abutting portion receives from the inner circumferential surface of the shaft; and - an integrated member which integrates together the sleeve, on an outer circumferential surface of which a thread groove (13d1) is provided, the annular portion, the flexible portion, and the abutting portion provided such that a gap is provided between the sleeve and the abutting portion; - a nut screwed together with the thread groove (13d1) and disposed between the sleeve and the abutting portion, a tapered surface (13b3) provided on an outer circumferential surface of the nut abutting the abutting portion; and - a spacer ring adapted to be attached to the center vent tube, and an outer circumferential surface of the spacer ring abutting an inner circumferential surface of the sleeve; wherein a plurality of the flexible portions and a plurality of the abutting portions are discretely provided along a circumferential direction of the sleeve, and the abutting portions are adapted to be pushed outward in the radial direction of the center vent tube toward the inner circumferential surface of the shaft by the tapered surface (13b3). - an annular portion adapted to be coaxially provided with the center vent tube in an outer side of the center vent tube in a radial direction thereof; - a flexible portion protruding downstream from an edge portion of the annular portion in an outer side in the radial direction thereof; - an abutting portion connected to the flexible portion, and adapted to abut an inner circumferential surface of the shaft; - a cylindrical sleeve integrated with the annular portion at an upstream end of the cylindrical sleeve, adapted to surround the center vent tube from the outer side in the radial direction of the center vent tube, and adapted to be supported by a reaction force that the abutting portion receives from the inner circumferential surface of the shaft; and - an integrated member which integrates together the sleeve, on an outer circumferential surface of which a thread groove (13d1) is provided, the annular portion, the flexible portion, and the abutting portion provided such that a gap is provided between the sleeve and the abutting portion; - a nut screwed together with the thread groove (13d1) and disposed between the sleeve and the abutting portion, a tapered surface (13b3) provided on an outer circumferential surface of the nut abutting the abutting portion; and - a spacer ring adapted to be attached to the center vent tube, and an outer circumferential surface of the spacer ring abutting an inner circumferential surface of the sleeve; wherein a plurality of the flexible portions and a plurality of the abutting portions are discretely provided along a circumferential direction of the sleeve, and the abutting portions are adapted to be pushed outward in the radial direction of the center vent tube toward the inner circumferential surface of the shaft by the tapered surface (13b3).