PURPOSE: To provide a pressure kneader with low structural height and reduced weight which has a mixing tank shut off an outer area and is capable of doing the pressure kneading in vacuum, as a pressure kneader with a pressure lid which lifts up and down vertically with a material charging port provided above the mixing tank.

CONSTITUTION: The entire machine height of a pressure kneader is reduced by separating a means for driving a pressure lid 3 to be inserted into and removed from a mixing tank for pressurizing from a means for lifting up and down the pressure lid which forms required space for charging a material or reversing the mixing tank in the upper part of the mixing tank, and using their respective alternative means. In addition, the lower edge flange of an enclosure lid 4 which stores encircling the pressure lid from above descends and comes into contact with the upper edge flange of the mixing tank 2. Under this state, these flanges are tightened by a clamp 8 to create an airtight condition, so that the air is exhausted from the interior to obtain a vacuum.