PURPOSE: To perform a clamping pressurization steadily in conformity with a mold height and to simplify a construction, by a method wherein a pressurizing head is mounted to an upper end of a pressurizing rod so that its height can be adjusted in conformity with the mold height.

CONSTITUTION: A pressurizing head 20a, being of a nut structure, is installed to a top end of a pressurizing rod 20, and through the formation of a screw part 20b in the pressurizing rod 20, the pressurizing head 20a screws the screw part so that it can freely spin and elevate. In case upper and lower forces 1a and 13a having a high mold height are used, a pressurizing is conducted on both sides without any trouble through raising of the pressurizing head 20a to the top end of the pressurizing rod 20. In case upper and lower forces 1b and 13b having a lower mold height are used, the pressurizing head 20a is lowered corresponding to said height.