PROBLEM TO BE SOLVED: To easily realize desired twisting process, and to realize twisting process of special form in cross section.SOLUTION: When a metal pipe 5 is transported by a recess forming roll pair 4a, a reference roll pair 4b, and a threading roll pair 4c, in this order, the metal pipe 5 whose cross section is almost circular is pressurized toward the inside of pipe by the recess forming roll pair 4a, to form a recess 53. The metal pipe is made to be abutted in a predetermined direction by the reference roll pair 4b, and rotated in the outer periphery direction of the pipe from the abutment surface of the reference roll pair 4b, according to a desired twisting angle relative to a pitch in pipe axial direction from the reference roll pair 4b. The metal pipe 5 is twist-processed by pressurizing the metal pipe 5.
