shaft 44 rotates four times per one rotation of the main shaft 252 so that the weft guide pipe 53 rotates around the drum 48 thereby to wind up the weft yarn 10 on the drum 48 thus under rotation of the weft guide pipe 53 the weft yarn 10 of a predetermined length required for one weft picking is wound on the drum straight section 48b between the engaging pins 155 and 156 by a time point immediately before the weft picking when the weft picking step has come the mechanical valve 225 is first opened to eject pressurized air from the weft inserting nozzle 17 immediately after this the engaging pin 156 is withdrawn from the hole 161 to release the weft yarn 10 so that the weft yarn 10 is drawn or pulled by the air ejection from the weft inserting nozzle 17 and inserted through the guide opening 197 of the picked weft yarn removing pipe 196 into the weft guide groove 187 in timed relation to this the mechanical valve 233 for the auxiliary nozzle 189 is opened slightly before the tip end section of the weft yarn 10 passes by the auxiliary nozzle 189 thereby ejecting pressurized air from the auxiliary nozzle 189 thus the tip end of the weft yarn 10 is successively blown away along the weft guide groove 187 under the influence of air jets which are successively ejected from the auxiliary nozzles 189 disposed along the weft guide groove 187.