To reduce tension, which is increased when a quantity of a residual yarn on a yarn feeding bobbin is decreased, of the yarn.

A balloon controller 10 is provided with a cylinder 11 moving the balloon controller 10 vertically along the axial direction of a yarn feeding bobbin B and a photoelectric sensor 12 detecting a chase part C in the yarn feeding bobbin B. When the balloon controller 10 is shifted to the lower limit by means of the cylinder 11 according to a release of yarn from the yarn feeding bobbin B, a unit controller 7 feeds a stress reducing command to a tensor 1 if the photoelectric sensor 12 detects no chase part C. Afterwards, the unit controller 7 feeds a speed reducing command to an inverter 6 so as to lower a rotational speed of a driving motor 5.