PURPOSE: To obtain a cylindricity with a high degree of accuracy, and to make it possible to carry out a polishing process with a highly accurate surface roughness and a highly accurate roundness, by changing the position of a round rod between the outer peripheral end side and the center end side of discs or lapping plates after the discs or the lapping plates being rotated by a predetermined number of rotations.

CONSTITUTION: Upper and lower lapping plates 14, 4b are rotated in opposite directions. A carrier plate 8 is rotated by a predetermined number of rotations to polish round rods 16, and a slide head is elevated after the rotation of the carrier plate 8 being stopped. Then the diameter of each round rod 16 decreases along the direction from the inner peripheral end to outer peripheral end of the carrier plate 8, that is, the round rod 16 is tapered. Then each round rod 16 is taken out from the associated elongated hole 9, the direction of the round rod 16 being changed so that the inner peripheral side end of the rod 16 is positioned at the outer peripheral end side of the carrier plate 8, and then the rods 16 are returned into the elongated hole 9. During second polishing, the tapered section of the round rod 16 is corrected, and therefore, the round rod 16 comes to have a highly accurate roundness. Further, the outer surface of the each round rod is made into uniform contact with the upper and lower lapping plates 14, 4b, thereby it is possible to have a highly accurate surface roughness and a highly accurate roundness.