PURPOSE: To utilize the bottom of a bottomed material tube as it is and to improve its yield by providing a bottom thickness adjusting device on the upper edge of an outer die for containing a billet.

CONSTITUTION: A billet is contained in an outer die 5, and a liner 6 for adjusting bottom thickness is provided in the upper part of the billet and outer mold 5. Under this condition, a mandrel 7 is thrusted in by a vertical hydraulic press. The bottom thickness of a material 4b to be pierced is adjusted by the bottom thickness adjusting liner 6. A hollow cylindrical material 4b thus obtained is hot reduced and a bottomed material tube is obtained. By this way, a tube having closed an end and having uniform mechanical strength as a whole is manufactured.