PURPOSE: To obtain an elbow of high quality and high dimensional accuracy having smooth surface without requiring complicated processes by inserting a tubular material into a curved hole provided in a die and supplying and pressing a spherical body in the tubular material.

CONSTITUTION: The tubular material 20 is inserted from the end of curved hole 2 of the die 1, and the rear end of the material 20 is pressed in the curved hole 2 by the first plunger punch. Then, the first plunger punch is pulled out, and a spherical body 6 made of steel slightly smaller in diameter than inner diameter of the material tube 20 is supplied from rear end of the tube, and rear end of the material 20 and spherical body 6 are pressed in the curved hole 2. The material 20 is advanced and plastic deformed. Then, a spherical body 8 having the same diameter as the spherical body 6 is supplied in the material 20, and the material 20 and spherical body 8 are pressed in the curved hole 2 by a plunger punch having longer large diameter part. The material 2 is plastic deformed along the shape of curved part 2a. When an additional spherical body is supplied, and the material 20 and spherical body are pressed in by the fourth plunger punch, the material 20 is pressed in the curved hole 2 until it comes into contact with a stopper fitting 3, and plastic deformed to final shape with its inner face held by the spherical body.