To prevent oozing of a kneading material out of a seal part by a kneading interior pressure in addition to preventing the sealing surface from wearing down.

This device is equipped with a sealing pressure imparting circuit E imparting a sealing surface pressure to a seal device of a rotor contained in a kneading chamber, a drop door drive circuit C having a first a solenoid valve 39 for a drop door which controls operation of a drop door 15 closing a bottom surface of the kneading chamber and a power circuit A supplying a pressure oil to sealing surface pressure imparting circuit E, and the drop door drive circuit C. Then, the sealing surface pressure imparting circuit E is connected to the pressure oil supplying circuit of the power circuit A and the sealing surface pressure imparting circuit E is provided with a second solenoid valve 44 for imparting the sealing surface pressure with on-off control of a plumbing of the pressure oil by interlocking to the first solenoid valve 39 for the drop door of the drop door drive circuit C. The pressure oil is supplied by the second solenoid valve 6 for imparting the sealing surface pressure after an elapse of a predetermined time, after the first a solenoid valve 39 for the drop door is controlled to open the drop door 15.