To prevent warp fuzz from arising and also to improve weaving performance by markedly cutting out redundantly splashed water with a water diffusion prevention guide placed between a nozzle and a cutter located on the side of the nozzle.

By installing a water diffusion prevention guide 1 made of a noncorrosive metal (e.g. stainless steel) between a nozzle 2 for a water jet loom and a cutter located on the side of the nozzle, redundantly splashed water in inserting a weft is cut out to decrease the quantity of water striking on a warp. The guide 1 has a notch which is 3-13 mm long and 5-20 mm wide, opens toward a cloth fell and is followed by a bore having a diameter of 5-15 mm through which the weft passes.