To obtain a hollow shape material having different inner diameter and outer diameter in a vertical cross section and a desired light wt. by making each of plural extrusion members in the dead state or in the shifting state in the extrusion working.

A billet 22 having a hollow part is inserted into a through-hole 10A of a container 10. A mandrel 17 is inserted into the holow part of the billet 22 and this wedge-like tip part 17B is arranged so as to position to the outside of a billet extrusion hole 9. A punch 19 is inserted into the container 10 and abutted on the billet 22. Dies 11, 12 and the mandrel 17 are made to the dead condition, and at the time of extruding the billet 22 by pushing the punch 19 frontward, a pipe material 24 having the same inner diameter in the vertical cross section as the outer shape of the vertical cross section of the mandrel 17, is obtd. While shifting the mandrel 17 rearward and the die 12 upward, the punch 19 is pushed frontward and then, at the time of extruding the billet 22, the pipe material having the inclination gradually formed slenderer from the one end part to the other end part on the side wall part, is obtained.