PURPOSE: To secure the sanitary performance by diffusion-welding or blazing- welding a plurality of erosionproof members having each recessed groove on the opposed surface and forming the above-described recessed groove as the fluid flow passage inside a structure.

CONSTITUTION: An installation flange part 3 is formed on a column shaped member 1, and a through hole 5, back facing hole 5a, and a communication groove 6 are formed on a body member 4. Further, a closed groove 8 and a closed hole 9 are formed on a large diameter bottom plate member 7. A plurality of column shaped members 1 are fitted on the back filling hole 5a on the body member 4, and fixed through TIG welding. Then, the back side of the body member 4 is positioned on the bottom plate member 7 so that the grooves on the opposed surfaces are allowed to coincide or a through hole 5b and the semispherical closed hole 9 are allowed to coincide, and the peripheral part is sealing-welded through the electronic beam welding. Then, diffusion welding is carried out so that the inside groove is not deformed and the strong joint is obtained on the joint surface. Accordingly, the pressureproofness is improved, and the sanitary performance can be secured.