fluid chamber 22 is larger than that of the branch passage 19 formed within the upright guide member 13 because the inner wall of the fluid chamber 22 bulges towards the inner wall of the upright guide member 13 a plurality of fluid blowing holes 23 four in the illustrated embodiment are formed on the inner surface of the upright guide member 13 which surface faces the weft inserting direction as illustrated in fig4 and 5 so that air flow fed from the base fluid passage 16 and branched into the branch passage 19 and the fluid chamber 22 formed within the upright guide member 13 is blown as auxiliary air jets through the four fluid blowing holes 23 towards the central axis of the weft inserting opening 14 the first embodiment according to the present invention operates as follows the air flow fed through the base fluid passage 16 is smoothly branched by the branching wall 17 into the branch passage 18 formed within the arced guide member 12 and the branch passage 19 formed within the upright guide member 13 without encountering any substantial resistance and the branched air flows are blown through the fluid blowing holes 21 and 23 accordingly when the air flow is branched the air flow speed is not reduced and turbulence is not introduced into the air flow or the effects are reduced from those caused by conventional guides.