PURPOSE: To stabilize the accuracy of pattern matching of weft yarns by nipping a weft yarn regulated to a prescribed insertion length using a picking system of the top of a spatula, bringing it into a shed, releasing it at a prescribed position and subsequently beating up.

CONSTITUTION: In a foil thread insertion type weft insertion unit for forming a pattern of weft yarns on a woven fabric in kasuri (a Japanese woven fabric) weaving, foul thread weaving, etc., a weft yarn having a prescribed length regulated by a sensor 10 through a weft yarn-conveying system 60 is nipped using a nipping system 20 at the top of a spatula 30 inserted into a shed. The above-mentioned spatula 30 is then moved back and the above-mentioned weft yarn is brought into the shed. The weft yarn is released from the nipping system 20 at a constant position and beating up is subsequently carried out, thus interweaving the weft yarn at a constant position of the warp without fail.