To improve boring workability by fixing an additional nozzle by a means such as stroke caulking or the like, and simplifying the dimensional management for a small inlet provided in the additional nozzle.

An additional nozzle 18 is fitted in an accommodating hole 17C of an adapter 17 and temporarily stopped. In such a condition, an injection valve is driven to jet a liquid from a jet nozzle 18D of the additional nozzle 18, and a jet flow of the liquid is measured. According to the measurement result on the jet flow, caulking load corresponding to the target flow is computed. After that, a caulking punch is pressurized in the axial direction toward the accommodating hole 17C of the adapter 17 by driving force corresponding to the caulking load. Thus, a caulking part 17F is formed on the upper end side peripheral wall of the accommodating hole 17C, and each small inlet 18E of the additional nozzle 18 is a little reduced in diameter by the caulking load at this time, thereby adjusting the jet flow.