WATER JET NOZZLE

PROBLEM TO BE SOLVED: To accelerate cavitation within a cup-shaped cavity part at the front end of the ejection hole of a nozzle. SOLUTION: The water jet nozzle which injects a high-velocity water jet 14 from the ejection hole at its center, is provided with the cavity part 11 of an approximately cup shape at the front end of the central ejection hole and destroys and removes deposits or finely grinds and decomposes the hazardous materials in the water, is so constituted as to eject a low-velocity water stream 22 from the outer side of the cavity part toward the high-velocity water jet at such an angle θ at which this low-velocity water stream runs backward with respect to the high-velocity water jet 14 from the central ejection hole 19. Additionally, the low-velocity water stream 22 is ejected from the plural ejection holes opened at the inside wall of the approximately cup-shaped cavity part. The low-velocity water stream 22 is ejected from the slit-like aperture 20 disposed at the inside wall of the approximately cup-shaped cavity-part.