PURPOSE: To obtain such a covered composite yarn that a portion where multi- filaments are separated from each other is not observed, by specifying the inner passageway of a straight tube for passing the multi-filaments therethrough and the arrangement state of compressed gas-blowing holes.

CONSTITUTION: The inner diameter of a straight tube 1 for passing a multi- filament yarn therethrough is 4-12mm, and a plurality of compressed gas-blowing holes 2a-2d are arranged at plural positions to open the holes so as to generate the circulation flows of the gas, respectively, in the tube. The blowing holes 2a-2d are distributed toward the periphery of the tube and at an interval of ≥5mm in the longitudinal direction of the tube.