PURPOSE: To simplify the structure of a discharge gate, to avoid localization of a material during discharging and to discharge a large amt. of the material.

CONSTITUTION: A discharge orifice for discharging a material is provided along the axial direction of kneading shafts 14 and 14' in the neighborhood of the intermediate part of the lower part of a kneading tank 13 consisting of a pair of trunks of a biaxial mixer 11. A discharge gate wherein the central part is formed into a hill shape is provided in the discharge orifice and this discharge gate is divided along the axial direction of the kneading shafts 14 and 14" at the position deviated to the side from the top of the hill shape and the side contg. the top of the hill shape is made a large gate 23 and another side is made a small gate. These are respectively fixed on the side of the discharge orifice and are made freely switchable.