To provide a locking nut which can apply a bending load to a bolt such that an eccentric load is not applied to a nut, can particularly be cold-forged so as to exhibit a powerful loosening stopping effect.

In the locking nut which comprises a head 1 and a flange 2 which is integrated with the head and has a larger diameter than the head, a recess portion 3 is formed in the flange. The bottom surface 2a of the flange is formed in taper shape from one edge A to other edge B opposite thereto. The bottom surface 3a of the recess portion is formed in parallel to the top surface 5 of the head.