To provide a yarn winding device that minimizes occurrences of sloughing during unwinding from a yarn feeding bobbin even when yarn winding is performed at a high speed, thereby increasing package production efficiency.

A yarn unwinding assisting device 20 of a yarn winding unit 1 includes a movable cylinder 31 that, during yarn unwinding from the yarn feeding bobbin 8, is to be put on to cap an end part on a side from which a yarn is unwound of the yarn feeding bobbin 8 to thereby regulate a bulge of a curved path of the yarn. An inner diameter of the movable cylinder 31 is≥28 mm and ≤30 mm.