Provided is a method of phasing a threaded grinding stone, as well as a device therefor, the aforementioned method and device being such that contact or non-contact of a threaded grinding stone with a disk dresser can be detected with high accuracy, with the result that the phasing of the threaded grinding stone can be accurately performed. For the purpose of achieving the above, a threaded grinding stone (14) is phased with respect to a disk dresser (32) prior to the engagement of the threaded grinding stone (14) with the disk dresser (32) during dressing. In performing this phasing, it is determined whether or not the threaded grinding stone (14) contacted the disk dresser (32), on the basis of a voltage (V) which is commensurate with the amplitude of the elastic wave generated in the threaded grinding stone (14) at the time when the threaded grinding stone (14) contacted the disk dresser (32). In a case where the voltage (V) does not exceed a threshold value (Vo) even if the threaded grinding stone (14) contacts the disk dresser (32), then the rotational speed of the disk dresser (32) is increased, with the result that there is forcibly created a situation where it is determined that contact occurred. Subsequently, the threaded grinding stone (14) is positioned, on the basis of the resulting phase thereof, in an intermediate phase where the aforementioned engagement is feasible.