PURPOSE: To prevent a parison from being damaged or set in an oversupplied condition by using a clamping device for holding the tip of the parison of a polymer material extruded from an extrusion head between a flat plate surface and a spherical surface.

CONSTITUTION: A clamping device 20 is composed of a holding member 12 and a receiving member 14 installed in a mutually opposite position, on the lateral face of a lower force 6a. The holding member 12 is composed of a semispherical holding member 14 of a spherical tip and a drive cylinder 18 for driving the semispherical holding part 16. The receiving member 14 is composed of a guide-in slope 14a opened toward an area outside an upper lateral part and a receiving flat plate face on a lower lateral part. When setting a parison 4 on a cavity face vertically, the tip part of the parison 4 is held between the flat plate face 14b and the spherical surface 16, and the parison 4 is freely rotated downward and slightly freely rotated horizontally with the help of the grip part, if the parison 4 is curved downward so that it lies along a shaping groove part 8. Consequently, the parison does not become a float at a gripping position and near the clamping device 20 and the parison 4 follows the shaping grooved part 8 easily. Thus setting the parison is facilitated.