PURPOSE: To obtain the titled filament extremely stably and uniformly, by extruding a polymer in a molten state through a spinneret having a specific introduction hole and a distribution plate, cooling it, providing it with a finishing oil to bundle it, winding it.

CONSTITUTION: A polymer (preferably polyester type polymer having 1.40W1.60 relative viscosity) is extruded in a molten state by using a spinnerent having one introduction hole to introduce the polymer into its center, wherein a distribution plate having plural distribution holes to distribute the polymer into plural extrusion holes of spinneret plates which are radiately brnahced from the introduction hole is set in such a way that it is brought into contact with the tops of the spinneret plates. The spun yarn is sprayed with cooling air flow right below the spinneret, cooled, provided with a finishing oil at a position 50W 130cm below the bottom of the spinneret, bundled, and wound to give extremely thin multifilament having ≤1.0 denier of single yarn.