Then, a fluid such as compressed air or a mixture of nitrogen and pure water is ejected to the substrate W via the communicating holes 402 a, 404 a of the suction portions 402, 404 to release the substrate W from the top ring 300. [0256] The polishing liquid Q used to polish the substrate W tends to flow through the gap G between the outer circumferential surface of the elastic pad 336 and the ret