PURPOSE: To provide a high accuracy of locking nut which generates no balance collaps in a decomposition and a reassembling time, and has no risk of generating a deflection of the end face, and a deformation of the shaft, by the fastening condition of a bolt.

CONSTITUTION: A locking nut 4 is composed of the first nut 4A with a large thickness, and the second nut B whose thickness is thinner than the first nut 4A, screw holes 4a are provided on the circumference of the first nut 4A, at the positions divided into 12 equal parts, for example, while bolt holes 4b corresponding to the screw holes 4a are provided on the circumference of the second nut 4B, at the positions divided into 6 equal parts, for example, and the second nut 4B is fastened tentatively by a bolt 5 by slipping the phase one pitch (30°) to the near side, to the first nut 4A, when the locking nut 4 is assembled. By measuring the clearance in this time, and after cutting out the right end surface of the nut 4B to make the clearance in an ideal fastening margine by a planing and the like, it is fastened fully by the bolt 5.