PURPOSE: To extrude a pipe small in eccentricity and excellent in the accuracy of thickness deviation by piercing a billet by thrusting a mandrel into the billet charged in a container and revolving the mandrel during piercing.

CONSTITUTION: At the time of piercing, the billet 2 is pierced while revolving the mandrel 3, pressurized by moving the mandrel 3 and dummy block 13 in the back and forth directions while continuing the revolution of the mandrel 3 and extruded into a pipe shape from between the mandrel 3 and the hole 5 of a die 4. Since the mandrel 3 is revolved, the eccentricity of the hole of the billet 2 is reduced and furthermore the pipe having small thickness deviation is obtained because of extrusion while revolving the mandrel 3.