PURPOSE: To enable releasing of fibers which form a yarn without applying twist to the end of yarn by blowing compressed air on a narrowed portion of the yarn fixing wall surface of an untwisting pipe internal wall after laying the end of yarn to be processed along the narrowed portion to release the fibers which form the end of yarn into individual fibers.

CONSTITUTION: A yarn end 16 is stored by means of sucked air, in a yarn holding portion 20, which forms a narrowed portion formed by internal walls 18 and 19 of an untwisting pipe 7, and positioned in the yarn holding portion 20 without any random action. In this condition, when compressed air is blown out from an untwisting on air blowing port 12 provided in a wall surface 21, etc., opposed to a yarn to be processed, the blowing port 12 catches the end of yarn to be processed 16 very precisely because it is opposed to the end of yarn to be processed 16, and the compressed air is blown against it. Because the compressed air is blown directly and obliquely to the end of yarn to be processed 16 and also the yarn is held securely by the yarn holding section 20, fibers which form the yarn end 16 an be released securely without twisting the yarn.