To provide a joining method in which there is no leakage of fluid between a metal tube and other members.

A motor 8 rotates a metallic glass tube 1 and stainless steel tubes 2a and 2b attached to a jig 4 through a motor rotary shaft 9, a flange 6b, and a flange 6a. 12 is a nickel anode. The metallic glass tube 1, the stainless steel tube 2a and 2b attached to the jig 4 are put in a nickel electroforming tank 13 that puts in an electrolytic solution 11 for nickel electroforming. They are rotated in the electrolytic solution 11 for the nickel electroforming by motor 8, and an electroforming layer 14 is formed. In this case, the electrolytic solution 11 for the nickel electroforming in the nickel electroforming tank 13 is warmed to about 45°C. When the nickel electroforming layer 14 reaches a prescribed thickness, the switches of a power source 10 and the motor are turned off. The flanges 6a and 6b are separated, the jig 4 or the like is taken out from the nickel electroforming tank 13, the connected metallic glass tube 1 and stainless steel tubes 2a, and 2b are taken out of the jig 4 made of a resin, and resist is removed by a solvent or the like afterwards.