To produce a high-speed jet water stream responsive to an ultrahigh- speed operation of a loom and excellent in coherency in a water jet nozzle for carrying out the weft insertion of a weft yarn.

This water jet nozzle for a high-speed loom is obtained by forming a cone angle θ of an orifice member at 15-35° and thereby producing a jet water stream suitable for an ultrahigh-speed operation of ≥1,200 rpm in the water jet nozzle having a needle and the orifice member coaxially arranged in the interior of the nozzle body and equipped with at least one stabilizer on the upstream side of the orifice member. The length 1 of the orifice member protruded from an outlet corner part of the orifice member to the needle tip is regulated so that a value of Y in the formula 1=θ/360°×10L×Y is 0.25-0.7. Thereby, the protruding length 1 can be determined by the calculation and a jet water stream excellent in conveying force remarkably excellent in coherency is produced.