PURPOSE: To adjust and control the surface pressure of contact face of a top force and a bottom force at the time of clamping by providing a hydraulic mechanism for adjusting the contact face of the top and bottom forces between a toggle mechanism and a movable platen of a vertical molding machine.

CONSTITUTION: A movable platen 5 connected with a toggle mechanism 7 is supported by a hydraulic mechanism 17 consisting of a hydraulic cylinder 18 and piston rods 19, and unevenness of clamping strokes generated by the different length of respective toggles of the toggle mechanism 7 is absorbed and the surface pressure of contact faces of top and bottom forces 2 and 6 is adjusted to be equal by applying hydraulic pressure equally to respective hydraulic cylinders 18 after the toggle mechanism 7 is stretched out and clamping stroke is completed at the time of clamping. Also, mold thickness adjustment is not required to be carried out separately to a little variation of thickness of the top and bottom forces 2 and 6, and the variation can be absorbed within a stroke range of piston rods 19 of respective hydraulic cylinders 18.