PURPOSE: To shorten a process for the titled manufacture and to manufacture a large diameter branch pipe by pushing out a mandrel to pierce a branch pipe after press forming a metallic plate into a U-shape by a male die and performing the U-shape forming and piercing operations continuously.

CONSTITUTION: A male die 5 and a mandrel 4 are fitted in a unified construction into female dies 2 and 3, to press form a blank material 1 into a U-shape. Next, the material 1 is pierced by pushing out the mandrel 4, to form a branch pipe 7. Accordingly, the pressing and piercing operations are continuously performed. Next, after removing the male die 5, mandrel 4, and female die 2, an upper half of the material 1 is press formed into a semicircular shape by a female die 8. A seam part is finally welded to obtain a branch pipe fitting. By this method, the process is shortened; and a branch pipe fitting for a large diameter pipe impossible to manufacture as a seamless pipe, can be manufactured.