To provide a yarn slackening-reducing device suppressing tension fluctuation generated in a roller part, and sufficiently securing a yarn storage quantity.

The yarn slackening-reducing device 12 includes a roller part 42. The roller part 42 includes a winding area 60 for winding a spun yarn 10, and a base-end-side flange part 61 connected to an upstream end of the winding area 60, and formed to be larger in diameter than the winding area 60. The base-end-side flange part 61 is formed to be tapered toward a connection part with the winding area 60. In the base-end-side flange part 61, a tilt angle of a tapered part with respect to a virtual surface 63 is set to be 45 degrees or more at the connection part with the winding area 60, the virtual surface 63 being formed by extending a surface of the winding area 60 toward the base-end-side flange part 61 side.