METHOD FOR PRODUCING SYNTHETIC FIBER

PROBLEM TO BE SOLVED: To provide a method for producing ultrafine synthetic fibers having a single fiber fineness of 1.5 dtex or less by melt spinning, which can suppress variations in 15% stress and can suppress variations due to nonuniformity in dyeing among filament groups each including multiple filaments in the same spinneret.SOLUTION: In a method for producing synthetic fibers, a thermoplastic resin is melted, and filament groups extruded from a spinneret 2 in an annular arrangement are annularly cooled with cooling air blown out from the outer circumferential side of the filament groups toward the center side of the filament groups using an annular cooling device 5 provided below the spinneret. The filament groups are run in a spinning chimney 62, and an oil solution is applied to them. The method for producing synthetic fibers satisfies the following conditions (A) to (C) at the same time: (A) the spinning chimney is provided below the annular cooling device; (B) an oil solution-applying device 7 is present in the spinning chimney or below the spinning chimney; and (C) the filament groups are surrounded by the spinning chimney over the entire circumference.