PURPOSE: To prevent parison from deforming by a method wherein the holding of the parison is performed not by the conventional holding by its own strength, which causes defect such as drawdown, but by the holding not by its own strength.

CONSTITUTION: The parison 2, which is extruded from a crosshead die 1, is held by the buoyancy of the liquid, the specific gravity of which is regulated so as to be near1y equal to the specific gravity of the parison, resulting in preventing the drawdown of the parison 2 from developing.