PURPOSE: To obtain a slack tube capable of carrying out smooth yarn ending regardless of yarn quality and spinning speed by arranging the end on an air suction side of a slack tube having fine and long slit-like and flat yarn storage hole in a suction duct and, in addition, arranging a pressurized air jet nozzle along upper and lower parts of the yarn storage hole.

CONSTITUTION: In a slack tube 1 which is a yarn storage device for keeping and storing yarn Y spun while carrying out yarn ending motion by a yarn ending device of spinning machine, end part on air suction side of the slack tube 1 whose yarn storage hole 3 has a slit-like and flat cross-sectional shape slender in the vertical direction is arranged in a suction duct 2, and pressurized air jet nozzles 6, 7 are arranged along upper and lower parts of yarn storage hole 3 of the slack tube 1 in the air suction duct 2 and the jet nozzles 6, 7 are each connected, through each independent by arranged pressure control valves 8, 9 and electromagnetic valves 10, 11, to a pressurized air tank to smoothly carry out yarn ending regardless of yarn quality and spinning speed.