The first air guide groove (92) is formed at the bottom of a carrier (24) along the inner circumference of a circle whose radius corresponds to the maximum radius of a wafer (50). The air is supplied to the outer periphery of the wafer (50) through the first air guide groove (92) to form a pressure air layer (51) between the carrier (24) and the wafer(50). The formation of the pressure air layer (51) makes the air pressure applied to the wafer (50) uniform on the entire surface of the wafer (50), and thus, the wafer (50) can be polished under a uniform pressure force. The second air guide groove (94) is formed along the inner circumference of a circle whose radius corresponds to the minimum radius of the wafer (50), and therefore, the wafer (50) with an orientation flat or notch can be polished under a uniform pressure force.