draft device 10 from the periphery of the spinning nozzle 22 there are no obstacles to air blowing and the operation efficiency is high moreover compared to the conventional device since the pressurized air is injected from a position closer to the sliver s the sliver s can be blown off efficiently wherein the fiber of which is less prone to be blown off such as long fiber can also be blown off reliably furthermore according to the present invention by setting the force of the pressurized air from the air nozzle 40 to be weaker than the suction force of the spinning nozzle 22 of the twisting device 17 during piecing and selecting the blowing time of the pressurized air the joint thickness produced by the piecing can be controlled to be a desired value in other words by blowing pressurized air from the air nozzle 40 in a direction toward the sliver s from the draft device 10 which is to be inserted into the guide hole 20 of the spinning nozzle 22 and blowing off and eliminating a part of the fiber composing the sliver s the joint thickness can be controlled the force of the pressurized air from the air nozzle 40 was set to be weaker than the suction force of the spinning nozzle 22 because when the force of the pressurized air is stronger than the suction force of the spinning nozzle 22 all of the fiber of the sliver s fed from the draft device 10 is blown off without entering the.