To provide a filament yarn treating device capable of easily releasing and separating a twist yarn.

This device functions as follows, that is, feeding a high-speed fluid into an enlarged section 14 whose diameter is increased in the form of a taper shape through a nozzle section 10, vibrating a core member 3 by a suction which is generated near the inner wall of the enlarged section 14 because of Coanda effect when the high-speed fluid moves along the inner wall of the enlarged section 14, thus releasing and separating a fiber or the like fed between the inner wall of the enlarged section 14 and the core member 3.