Abstract: The present invention provides a hairiness suppressing device for an automatic winder that can perfectly balloon a spun yarn using a whirling current in a yarn passage. In a hairiness suppressing device (1) comprising a yarn inserting opening (9) that extends and opens in an axial direction of a yarn passage (8) in which a whirling current acts on a spun yarn, a wedge-shaped cover member (29) is provided that can open and close the yarn inserting opening (9). When a swiveling body (26) is swivellably moved to open the cover member (29), the yarn can be introduced into the yarn passage (8) through the yarn inserting opening (9). When the swiveling body (26) is swivellably moved to close the cover member (29), the whirling current in the yarn passage (8) is prevented from leaking from a side of the yarn passage (8).