PURPOSE: To damp the extent of ultra-high pressure water cutting operation by setting up a pool, filled up with a liquid, at the injection side of the ultra- high pressure water, and positioning a workpiece in an interval between a level of this pool and a nozzle, then cutting it.

CONSTITUTION: A water-jet processor is equipped with a nozzle 1 free of operation in the three-dimensional direction, and it is composed of a cutter 5 cutting a workpiece 4 into an optional form and a pool 3 filled up with a liquid 2 for damping use. A block 13 is interposed between both ends of the workpiece 4 and a support roller 11, thereby supporting the workpiece 4 horizontally. Next, operation of ultra-high pressure water and the nozzle 1 is started and the workpiece is cut into the specified form, but at this time, the ultra-high pressure water after cutting operation still maintains its breaking energy. However, this water pierced through the workpiece 4 is discharged into the liquid 2, so that it is dampable so efficiently as preventing its scattering.