A threaded member has a discontinuous helical thread ridge 15 on which a plurality of dividing portions 14 are formed in the middle. At least one of the discontinuous portions of the thread ridge 15, which is interposed between the dividing portions 14, is a locking portion 18 which is configured such that a flank angle of one flank, out of flanks on both sides of the thread ridge 15, is smaller than a flank angle of a flank corresponding to a basic ridge profile and at least part of the flank is disposed on an outside of the flank corresponding to the basic ridge profile.