PURPOSE: To surely pierce a yarn even into a complicatedly constructed narrow opening by centering a specific docking body constructed as a pin to an opening in a specific state.

CONSTITUTION: This device rotates a yarn piercing device 2 around an operating position into a spiral nozzle 1 in a spinning machine with a console 3 and a pin 32 of a docking body is made to centering in an opening 5. The pin 32 has a tapering outer peripheral face and has a groove opening at a side in a radius as a notch, then a hole connecting to a pressure source is provided in about parallel to an axial line of the pin 32, thus is opened at the tapering end face of the pin. The pin 32 is transferred in parallel to the axial line through an air pressure cylinder 17 and a supporter 15.