A twin-screw extrusion kneader includes: two rotating shafts provided side by side in an internal space; a rotational driving portion configured to rotationally drive the rotating shafts; and paddles provided in the rotating shafts and configured to rotate along with the rotating shafts so as to knead a kneading material. Further, the twin-screw extrusion kneader includes movable portions provided as members constituting a part of the housing, the part of the housing including an inner wall surface of the housing, the inner wall surface being opposed to radially outer peripheral surfaces of the paddles. The movable portions can be moved in a direction to approach the paddles and in a direction to be distanced from the paddles. The twin-screw extrusion kneader can control the viscosity of electrode paste by moving the movable portions.