The present invention relates to a lock nut which conventionally includes a large diameter part in which a coil spring is inserted into the lock nut and a coupling hole of which an inner circumferential surface is threaded, wherein a cover is detachably inserted and mounted into a nut body in a state in which an engagement protrusion is formed on the cover made of a material having a hardness less than the hardness of the nut body so as to prevent the coil spring from escaping to the rear end side, and the lock nut is provided with a fixture for fixing a fixing part of the coil spring using the cover and a main body.