To provide a manufacturing method of a metal pipe with a branch pipe which is comparatively liable in taking into consideration about environmental measures, by which a high branch pipe is obtained and the thickness distribution of the branch pipe is uniformized.

In a process in which the branch pipe is formed on the metal pipe by hydraulic bulging, a stage in which the alkali metal salt of a higher fatty acid is coated on the surface of the metal pipe is included. By defining the coating quantity as being in the range of 0.05-10.0 g/m2, in spite of adopting the hydraulic bulging method, the pipe the heigh of the branch pipe of which is higher is obtained, and the thickness distribution of the branch pipe is also uniformized. So, the generation of the expansion of a pipe end is made possible, and the mixing of brazing material at the time of connection and lack of strength are prevented.