PURPOSE: To loosen the thread end part of a strongly twisted thread or stranded thread without inconveniently combing fibers by providing at least one saw- toothed insertion member as an auxiliary means for loosening the twist of the thread end part on the wall part of a fiber loosening pipe.

CONSTITUTION: A fiber loosening pipe 12 is provided with a slit 25 on the lower side of the inflow opening 20 of the wall part 12' of the pipe, the slit 25 is extended in the longitudinal direction of the pipe and the saw-toothed insertion member 26 is inserted inside the slit 25. The fiber loosening pipe 13 is provided with constitution mirror symmetric to the fiber loosening pipe 12. The slit 27 is arranged at the wall part 13' of the fiber loosening pipe 13 on the lower side of the inflow opening 21 and the saw-toothed insertion members 16 and 28 are similarly inserted inside the slit 27. In order to connect the two thread end parts, the prepared thread end parts 18 and 19 are pulled into the splicing passage 4 of a splicing head, made to pass through a blow nozzle there and connected by compressed air flowing into the splicing passage.