PURPOSE: To reduce operation cost and installation cost, by mounting a drive means due to oil pressure, a floating wt. and a cushion cylinder and reciprocally moving the floating wt. up and down by a hydraulic cylinder.

CONSTITUTION: A hydraulic cylinder 22 is guided by the guide 25 provided to a stand 24 to rise and fall. A floating wt. 21 is mounted to the lower end of the hydraulic cylinder 22 and a cushion cylinder 26 is arranged to the upper part of the rack 24. In this constitution, a raw material is charged from a charge port 27. Next, the hydraulic cylinder 22 is allowed to fall by the supply of oil pressure and the floating wt. 21 is allowed to fall to push the raw material in a chamber 23. The reaction force received from the interior of the chamber 23 during kneading by the floating wt. 21 is received by the high pressure air sealed in the chamber above the piston of the cushion cylinder 26. By this mechanism, a hermetically closed type kneader simplified in mechanical structure and easy to maintain and inspect is obtained.