PURPOSE: To prevent scales from adhering on the inside surface of a reaction kettle and to increase the stirring efficiency by pivoting the lower end of main shaft on the bottom face of inside of the kettle and providing the special blades to the edge part of stirrer provided to the main shaft to cause the upward force for the stirred soln.

CONSTITUTION: The lower end of a main shaft 1 which is hung down to the inside of a kettle 2 from a driving system 6 is pivoted on a pivotal part 8 of bottom face of the kettle 2 freely rotatably. A stirrer 3 having a shape wherein the edge part is positioned along the inside surface of the kettle 2 is fixed to the main shaft 1 and many blades 4 are provided to the edge part of the stirrer 3. The respective blades 4 are slanted so that the upper parts of the blades 4 are declined to the rear part of the moving direction (a) and the upward force is caused for the stirred soln. in accordance with the rotation of the stirrer. The convection in the up-and-down directions is caused for the stirred soln. by the slant of the blades 4 to increase the stirring effect. The parts of inside surface of the kettle 2 opposite to the stirrer 3 are smoothly finished and thereby scales are hardly stuck on the inside surface of the kettle to keep uniform heat conduction from a jacket.