To provide a thread deslackening device capable of preventing an impact force from being applied to a thread from a thread guard member even if an abrupt speed change is generated in the thread.

The thread guard member provided in the thread deslackening device includes a thread guard body 38, a flyer shaft, and an arm 84. The thread guard body 38 guards the thread. The flyer shaft is constituted to be relatively rotatable with respect to a roller. The arm 84 is fixed with the thread guard body 38, and fixed to the flyer shaft. The arm 84 has an elastic member 83 for absorbing an impact. The elastic member 83 is arranged in the vicinity of a connection portion between the flyer shaft and the arm 84.