PURPOSE: To perform simultaneous polishing of the upper and under surfaces of a work in machining removal amounts, being equivalent to each other, through one cycle of a polishing work by providing a difference in hardness between upper and lower surface plates.

CONSTITUTION: Carriers 4 to hold works 3 and perform planetary movement owing to a difference in the number of revolutions between a solar gear 5 and an internal tooth gear 6 are nipped between upper and lower surface plates 1 and 2. The upper and lower surface plates 1 and 2 are rotated in a reverse direction to each other. Machining liquid containing grinding grains are fed from the upper surface plate 1 side and a polishing work is applied on the upper and under surfaces of the work 3. In this case, a difference in a hardness is provided between the upper and lower surface plates 1 and 2. This constitution reduces production of a difference between machining removal amounts of the work 3 machined and removed by the upper and lower surface plates 1 and 2 and effects simultaneous polishing of the upper and under surfaces of the work 3 in machining removal amounts, equivalent to each other, through one cycle of a polishing work.