To provide a method by which a molding tube without cracks or breakage by molding a joined pipe comprising a plurality of metal pipes by fluid-pressure molding can be advantageously manufactured with excellent productivity.

A plurality of the metal pipes 10, 12 are coaxially abutted. The joined pipe 26 is obtained by executing friction stir welding to the abutting part 14 by relatively moving a rotary tool 20 circumferentially, in which a pin 22 is concentrically provided to the tip, after inserting the rotary tool to the abutting part 14 while rotating it. The molding tube 40 in a desired shape can be manufactured by expanding the joined pipe 26 obtained in such a manner with pressure of a non-compressive fluid body 38 filled inside the joined pipe.