PURPOSE: To improve rust resisting property of joined end parts, by softening the part between two points of the first metallic tube out of the first and second metallic tubes having insulating cover layer such as synthetic resin with an electrode inserting therein, and pressure welding the end of the second metallic tube having auxiliary conductor and enabling the both to be joined by resistance welding.

CONSTITUTION: For instance, conductive bars 4a, 4b are moved in longitudinal direction of horizontal frames 2' so that electrodes 5a, 5b are positioned at desired joining positions of horizontal frames 2' and vertical frames 3' of a fence. Locking devices 7 are moved similarly, and electrodes 5a, 5b are brought into close contact with inner peripheral face of the frames 2'. When the bars are connected to a power source, current flows as A→D, and a part of the frame 2' between electrodes generates heat, and insulating cover layer becomes soft. As the end of the frame 3' is pressure contacted to the layer 1 of this part, softened layer 1 is broken. Metallic part of the end of the frame 3' to which an auxiliary conductor is pressed in comes into contact with the metallic part of the frame 2' and current flows as A→B→C→D. As the end of the frame 3' is notched, load that pressure contacts the frame 3' to frame 2' is concentrated to one part. As the sectional area of the current path is small, a large amount of heat is generated, and the frames 2' and 3' are welded together with the layer 1.