PURPOSE: To improve machining speed and efficiency, by using a mixture wherein the granular bodies of a material whose volume is changed by the application of a magnetic field or an electric field is mixed with grinding granules as a polishing agent, applying electric field, magnetic field, and changing pressure, thereby performing the machining.

CONSTITUTION: A polishing agent is supplied to a polishing gap on a body to be machined 1 in which a polishing tool 2 is movably placed. In the polishing agent used in the gap, grinding granules are put in a machining liquid such as a machine oil and the like, and the granules of a material whose volume is changed by the action of a magnetic field is further mixed. TiC, W2C, and the like are used as the grinding granules. A magnetic strain material such as ferrite and Co steel is used as the granules whose volume is changed. The polishing agent is compressed into the polishing gap, pressure is applied by a spring 7, and lateral vibration is applied by a vibrating device 4. By the polishing action of the grinding granules compressed into the gap by the application of the pressure to the tool 2 and the body to be machined 1, the polishing machining is performed.