To solve the problem of easily causing hydrogen embrittlement when tensile residual stress exists, since intrusion of hydrogen depends on a metallic structure and a stress state of a metallic surface, due to causing the hydrogen embrittlement of reducing static strength and fatigue strength when the hydrogen easily intrudes in a metallic material.

A hydrogen embrittlement resistant characteristic of the metallic material is improved by generating a hydrogen resistant layer of hardly intruding the hydrogen in a metallic material surface, by introducing compressive residual stress by imparting local plastic deformation to a metallic surface by breaking impact force of cavitation bubbles caused when these cavitation bubbles break, by generating the cavitation bubbles by using a cavitation jet for generating the cavitation bubbles by injecting a high speed water jet into water.