PURPOSE: To enhance the working efficiency of a kneader containing a kneading mixer by providing large kneading function by an extruder.

CONSTITUTION: Rubbery matter G is extruded through an extrusion passage 22 but, since the extrusion passage 22 has an almost conical tapered shape, the rubbery matter G is stretched (stretch flow) in the axial direction of the extrusion passage while made fine when passed through the extrusion passage 22 to be kneaded. Since a large number of the extrusion passages 22 are provided, kneading based on stretch flow is performed at a large number of places and, since the rubbery matter G integrated within a casing is divided into many extrudates, kneading efficiency is enhanced.