PURPOSE: To obtain a highly strengthened miter bend by joining together plural pipe pieces, having each joining surfaces slanted to its axis, at their joining surfaces and applying a pressure in the formed bend to deform it in large quantities.

CONSTITUTION: Plural pipe pieces 1 having each joining surfaces 3 slanted to its axis are joined together at their joining surfaces 3, and a stiffening ring 2 provided with a clearance 4 is mounted on the intermediate part of each pipe piece 1. Then a fluid pressure is applied in the pipe bend 1, which is deformed to eliminate its edged joining parts, thereby each piece 1 is reformed into a perfectly round shape having uniform diameter and the ring 2 is simultaneously fastened to the piece 1.