PURPOSE: To facilitate assembling and reduce the generating rate of the failure of a nozzle body by a method wherein caulking is not employed to incorporate the main body of the nozzle.

CONSTITUTION: A recess 1a is formed in the tip end part of a nozzle tube 1 while the nozzle body 7 is fitted into the recess 1a. The nozzle body 7 is constituted by abutting a pair of nozzle composing bodies 8a, 8b against each other and an eddy current chamber 9 is formed in the nozzle body. A retainer ring 16 is attached to the tip end side of the recess 1a and a disc spring 17, elastically contacting with the nozzle body 7, is interposed between the retainer ring 16 and the nozzle body 7. According to this constitution, a strong external force will never be applied when the nozzle body 7 is incorporated and the deformation of the nozzle body 7 or the deformation of the eddy current chamber 9 may be prevented. Accordingly, the nozzle body 7 may be incorporated with a good accuracy.