Abstract: A locking bolt consists of a main bolt with a through hole extending axially along its center line, a deforming bolt rotatably mounted in the through hole in the main bolt, and a nut which is screwed onto the end of the deforming bolt. At least one slit is provided in the end of the shaft of the main bolt, and when the nut is tightened the deforming bolt expands the end portion of the shaft of the main bolt. At the end of the shaft the through hole in the main bolt is provided with a tapered hole portion of which the diameter decreases gradually from the tip of the shaft toward the head of the main bolt, and the head of the deforming bolt is tapered so that it fits into the tapered hole portion. When the nut is tightened, the deforming bolt jams the thread on the end portion of the shaft of the bolt against the thread of the bolt hole, and thereby prevents the bolt from becoming loose.