PURPOSE: To reduce operating cost and installation cost and to improve working environment, by performing the rising and falling driving of a floating wt. through a rack pinion and, at the same time, supporting the pinion by the cushion cylinder fixed to a frame.

CONSTITUTION: A raw material is charged in a hopper 33 from the raw material charge port 36 thereof. At this time, a cushion cylinder 26 is present at a raised position. Subsequently, a pinion 26 is rotated by driving a motor 29 to allow a rack 23 and the rod 22 and floating wt. 21 connected thereto to fall, and the raw material is pushed in a chamber 35. Since the reaction force of the floating wt. receiving from the chamber during kneading is received by high pressure air sealed in the chamber above the piston of the cushion cylinder 26, a cushioning property is held. At this time, a support stand 27 moves with the movement of the cushion cylinder 26, but the downward movement thereof is elastically limited by a rubber buffer 28. By this constitution, both of operating cost and installation cost can be reduced to a large extent.