PURPOSE: To make it possible change the acting point of fluid with extremely simple operation, by providing a removable or position-adjustable guide member for limiting the inserting position of end of a thread, on the surface of the thread end inserting opening in a nozzle pipe.

CONSTITUTION: Needle and lopper thread guides 40a, 40b and 41a, 41b are fixed to a front plate 18a, and the front ends of needle and lopper threads YP, YB which have passed through a thread splicing hole 1, are sucked into untwisting nozzles 5a, 5b. Compressed air is jetted from a compressed air jet hole 45b toward the center of the nozzle pipe 5b and inward of the nozzle so that the Z twist thread YB is subjected to the action of swirl stream F1 in the direction in which the Z-twist is loosened. After the thread turns along a semicircular hole 32b1, a direct-acting air stream 11 returns the thread to its original position. Accordingly, with the repetition of turning and attacking the end of the thread is untwisted. Further, the jetting direction of the compressed air is unaltered, and therefore, the Z-twist and S-twist may be loosened only by changing positioning members 29b, 30b in the nozzle openings.