Friction stir joining method and method

Object of the present invention is to provide an improved air tightness and water tightness of the joint portion of the joining method, it can also provide a bonding work efficiency, and rapid method of friction stir joining method. The friction stir joining method comprising a first step from the surface of permanently joined metal member (1) (12) of the metal side member (1,1) of the butt section (J1) and (1) from the back surface of the metal member (13 ) side butt portion (J1) of a second friction stir joining formal step, the joining method is characterized in that, in the second step, the formal engagement, so that rotating tool (B) was stirred a pin (B2) to enter the first official plasticized joining region (W1) formed in step, and simultaneously the friction stir.