Abstract: In the case of bending an outer pipe, a pressure die provided just in front of a bending section is provided with a groove, wherein the shape of the groove on the side far from the bending section is semi-circular and of which the diameter corresponds to that of the outer pipe before bending, while the shape of the groove on the side near the bending section is tapered semi-elliptically. With this, the cross-sectional shape of the outer pipe is caused to change into a substantially elliptical shape in which the outside of the section to be bent is tapered. The cross-sectional shape becomes substantially circular when bending is completed.