Abstract: An anchor bolt consisting of a shank screwed into a bore in a structural body made of concrete etc. having a screw thread with notches, and a root of thread between the screw thread. The entering flank and the trailing flank of the screw thread are defined by respective angles of inclination .alpha. and .beta. formed therefrom to the axis of the shank, the angle .beta. being smaller than the angle .alpha.. The root of screw is constituted by a carrying portion formed immediately after the trailing flank toward the unscrewing direction, and a tapered surface formed from the carrying portion to the root portion of the entering flank of the following screw thread, gradually increasing in diameter theretoward.