To provide a polishing device by a fluid grindstone capable of displaying comparatively strong polishing force, freely and stereoscopically deforming its shape in accordance with a shape of a working. surface and polishing a narrow and closed inner surface which a human hand and a solid grinding stone cannot enter.

A work is polished by using a polishing material 11 solidified or gelatinized in accordance with a shape of a working surface of the work and generation relative motion between the polishing material 11 and the work. It is carried out by giving mechanical vibration between the polishing material 11 and the work. The relative motion is generated by giving an alternating magnetic field in case of magnetic fluid free to control arrangement of abrasive grains by a magnetic field. Additionally, the relative motion is carried out by giving the alternating magnetic field in the case when the polishing material 11 is fluid containing the abrasive grains charged with plus or minus charge and it is solidified or gelatinized in the state of giving an electric field.