PURPOSE: To untwist the upper strand and the lower strand of a two-ply yarn in order in a simple structure by providing a rotor which has a pair of untwisting nozzles to untwist both ends of the two-ply yarn to be ended, and a rotating means to rotate the rotor so as to convert the untwisting direction.

CONSTITUTION: A rotatable rotor 12 which has a pair of untwisting respectively nozzles 26 and 27 to untwist separatively both ends YA and YB of a two-ply yarn Y to be ended, and a motor as a rotating means to rotate the rotor 12 so as to convert the untwisting direction are provided. And at first, the upper strand of the two-ply yarn Y is untwisted by the untwisting nozzles 26 and 27 respectively. Then, by rotating the rotor 12 180°, the facing directions of the untwisting nozzles 26 and 27 to the thread ends YA and YB are converted, and now the lower strand is untwisted. By only rotating the rotor 12 in such a way, the facing directions of the untwisting nozzles 26 and 27 to the thread ends YA and YB can be converted.