PURPOSE: To improve working efficiency by a method wherein the starting end part of a yarn unwound from a next winding ball is hooked around a yarn orderly unwound from a winding ball to form a knot hoop, and the knot hoop is closed for joining by means of an unwound thread terminal end detecting signal.

CONSTITUTION: Winding balls 2 are respectively pivotally supported to two unwinding devices A, a yarn (x) unwound from the one winding ball 2 is fed through a guide roll 48 to a connection device C, and is further fed as an adhesive yarn 1 to a corrugated board manufacturing process being a next process. A yarn Y from the other winding ball 2 is unwound in a similar manner describe above to the connection device C, where the starting end is hooked around the unwound yarn (x), and a knot is formed by a guide body 26 for waiting. When the terminal end of the yarn (x) is detected by a detector B, a rocking arm 7 of a detecting roll 8 is rotated downward, and a knot hoop is closed through a signal cable 42 to join the yarn Y to the yarn (x). This method eliminates the need to stop a device one, and enables improvement of working efficiency.