PURPOSE: To qualitatively foam a viscous material and prevent a stirring body from being removed from a rotary shaft by providing an auxiliary stirring body rotated by the stirring current of a material near the stirring body and stirring the material near the inside wall of a container and forming the length of the coupling section of the rotary shaft larger than the interval between the stirring body and the lower ends of inner vanes of the auxiliary stirring body.

CONSTITUTION: When a motor 2 is driven and a stirring body 10 is rotated at a high speed, a material is scattered toward the outer periphery, a stirring current rotated in the rotating direction as a disk-shaped section 10a while being convected is generated, and air is mixed for gradual foaming. The material collides with inner vanes 15b and extended sections 15e of an auxiliary stirring body 15, the auxiliary stirring body 15 is rotated in the same direction of the material, and outer vanes 15d stir the material near the inside wall of a container 5 and accelerate foaming. During the stirring action, the stirring body 10 is pressed downward by the material and is not floated. Since the length H of the coupling section 6b of a rotary shaft 6 is formed larger than the interval (h) between the upper face of the disk-shaped section 10a and the lower ends of the inner vanes 15b, even if the stirring body 10 is floated when it is rotated with no material filled, it is brought into contact with lower ends of inner vanes 15b, and it is not removed from the rotary shaft 6.