PURPOSE: To obtain yarns of higher mechanical strength without causing loss fibers, fine yarn defects or yarn breakages by providing a twist setting member between the 1st nozzle and second nozzle arranged in series.

CONSTITUTION: A twist setting member 13 is provided between the 1st nozzle 11 and the 2nd nozzle 12 of the air spinning unit 1 to prevent the false twist due to the revolving air flow from the 2nd nozzle from being transmitted to the 1st nozzle on the upstream side. Thereby, a sliver delivered through a pair of front rollers of a drafting device 2 passes the 1st nozzle in nearly a twistless parallel state, gradually increasing fibers with their tips being in nonrestraint. A core fiber bundle in nearly parallel state when passed through the twist setting member bundles due to false twisting by the 2nd nozzle and then is untwisted; in this process, the fiber with their tips being in nonrestraint state are wrapped tight on the core fiber bundle, forming wrapped fibers, thus obtaining bound spun yarns rich in wrapped fibers.