PURPOSE: To enable sufficient stirring and mixing even in a highly viscous material without generating undissolved lump, by providing a smither which stirrs and shears a material to be stirred and mixed at a high speed in a direction at a right angle to the flow of the material, in the passage of said material.

CONSTITUTION: The material charged from a material charging port 12 is stirred and mixed by inner and outer double blades 9, 8 and further strongly sheared, crushed and diffused by a smither 20 to be discharged from a discharge part 11. The aforementioned smither 20 is attached in a direction forming an angle of 45° to the center 24 of a tank and directly connected to a motor 23 and rotated at a high speed. Further, the smither 20 is provided with a sharp angle to strongly shear and crush the material to be mixed at a high speed with rotation between the smither 20 and a stator 21 and disperses the same in the wide range in front of said smither 20. By this mechanism, even a highly viscous material can be sufficiently stirred and mixed without generating the undissolved lump.