PURPOSE: To provide a flange for a vacuum to facilitate joining with a duct and reduce the occurrence of deformation, and reduce the part of parts and to provide a method thereof.

CONSTITUTION: The outer peripheral part 11 of a flange material for a vacuum of a stainless steel of which a flange 10 for a vacuum is formed has an outer peripheral part 11 joined with a disc member 12 of copper being approximately the same material as that of a duct 1 to form an integral cladding material. Thereafter, a mounting hole 13 corresponding to the outer shape of the duct is formed in the disc member 12, the end part of the duct 1 is inserted in the mounting hole 13 for joining through electron beam welding. After the outer peripheral part 11 of the flange 10 for a vacuum and the disc member 12 form a cladding material, processing of a seal surface 11a is practicable, joining with the duct 1 is effected by using the same material as each other, an ordinary joining method, such as electron beam welding and brazing, is applicable, a heat input is also reduced, deformation is also prevented from occurring, and the number of partiterns is also reduced.