PURPOSE: To surely untwine a yarn, even such a stiff yarn as flax or tight twisted woolen yarn, by furnishing a yarn end untwining nozzle, which is provided with a specific restricted space surrounding part of the yarn guide, in the neighborhood of both end openings of a yarn splicing hole.

CONSTITUTION: Pressure air from a flow line 51 in connection with a pressure air source is supplied to a flow line 53 formed in a bushing 50, and injected into a pipe 41 via a communication hole 54 and a hole 55 formed at the side face of pipe 41. Then the air passes a flow line 45 in an untwining nozzle block 42 to be injected into an untwining nozzle hole 33 from an injection port 46. The action of air stream injected into said nozzle hole 33 untwines the yarn end surely and turns the very tip of the yarn end into condition as reducing its diameter gradually, which provides suppression of diameter of the spliced part to lead to enhancement of the strength.