PURPOSE: To provide a method for machining a metallic fine tube so that the reliability for the mixture of a dust or a metal impurity can be improved and the production cost can be controlled.

CONSTITUTION: The internal part of a stainless fine tube 10 is filled with gaseous argon, the place to be bent of the fine tube 10 is heated to the state of a high temperature with an electric heaters 6-1 to 6-3 and 7, ad in this state, the fine tube is bent. In such constitution, the crack or the strain is hardly generated in a tube internal wall. Further, since gaseous argon is filled inside the tube, the generation of the corrosion like rust, etc., on the internal wall of tube due to heating the fine tube can be prevented, and the internal part of the fine tube can be also kept clean after bending. Therefore, even if the tube internal wall is not treated with an electrolytic polishing, the generation of the dust or the metallic impurity from the fine metal itself can be prevented, the reliability against the mixture of the dust or the impurity can be improved and the production cost can be also controlled.