PURPOSE: To enable marking to be automatically conducted in the vicinity of a seam at every yarn joining, by arranging an ink-immersed marking member at the yarn clamp position of a yarn joining device.

CONSTITUTION: Before conducting a yarn joining, both cut yarn ends YP, YB are guided onto a yarn joining device 2, and held by means of the fixed clamp 22 and the movable clamp lever 23 of a clamp device 9. At this instance, a yarn Y is pressed against a marking member 19 by means of a pressing frame 25 on the turning movable clamp lever 23. As a result, marking is done with the marking member 19 in the vicinity of the seam S of the yarn Y which is to be conducted with a yarn joining.