PURPOSE: To manufacture a seamless large diameter pipe with small driving power by subjecting a pipe material spirally to a process of bending part of said pipe material in its circumferential and axial directions to outer wide, and gradually expanding the same then bending the same to a straight pipe part.

CONSTITUTION: An inner roll 12 is restrained at an angle θ by a pair of guide rollers 41 disposed on both sides of the roll 12, and a pipe material 10 is passed through a clearance 36 at the angle θ with respect to the inner and outer rolls 12, 14 from the left direction. Then, it is driven by the rolls 12, 14 and moves in the direction of the clearance 38 while revolving. The unworked part 10A of the material 10 arriving at the clearance 40 is rolled by the tapered parts 16, 26 of the rolls 12, 14, by which the wall thickness is reduced and the material is bent to the outer side. Thereafter, it is bent to the inner side in the clearance 38 to form a straight pipe part 10C. The above-mentioned process is applied successively and spirally to the material 10, whereby the flow of the material in the circumferential direction is made easy and the need for large driving force is eliminated.