PURPOSE: To improve agitating performance of an abrasive by arranging magnets in the prescribed magnetic pole arrangement in respective magnet installing areas defined by a division line passing through the rotation center on an upper surface of a rotary body, following and moving the abrasive by magnetizing it by the magnets, and making the abrasive perform reverse motion complicatedly when a magnetic field acting on the abrasive is reversed.

CONSTITUTION: The first magnet installing area S1 and the second magnet installing area S2 are formed on an upper surface of a rotary body 4 by defining them by a division line L passing through the rotational center of the rotary body 4. A magnet 3a is arranged in a diameter directional outside area of the first magnet installing area S1 with the upper surface as an N pole, and a magnet 3b is arranged in a diameter directional inside area with the upper surface as an S pole. A magnet 3c is arranged in the diameter directional outside area of the second magnet installing area S2 with the upper surface as an S pole, and a magnet 3d is arranged in the diameter directional inside area with the upper surface as an N pole, respectively separately in the rotational direction to the magnets 3a and 3b. Thereby, a magnetic field is reversed instantly according to rotation of the rotary body 4, and magnetization of an abrasive is also changed, and complicated reverse motion is repeated, and agitation is caused.