To provide a polishing method capable of preventing its polishing yield from lowering by the deformation of a stationary plate in the polishing due to a change in temperature.

A polishing method holds constant the temperature of free grinding grains used in correcting an upper stationary plate and a lower one constituting a double polishing device, and also the temperature of free grinding grains used in matting both surfaces of a crystal substrate simultaneously with the device. Concretely, the temperature of free grinding grains is held constant by circulating cooling water in a vessel storing therein the free grinding grains to be used under circulation or by making the free grinding grains pass through a cooler prior to the feed thereof to the device.