To accurately detect the eccentricity of an optical disk by subjecting an objective lens to focus-servo control, and removing the radial vibration of the objective lens of the optical disk caused by the focus-servo control.
By rotating an optical disk DK while an objective lens 25 is not subjected to track-servo control, the eccentricity of the optical disk DK is measured according to the number of times by which an optical spot by a laser beam from a laser light source 21 crosses the track of the optical disk DK. The objective lens 25 is subjected to focus-servo control by a focus driving device 31, and a focus-servo control circuit 43. The radial displacement of the objective lens 25 of the optical disk DK resulting from the focus-servo control is canceled by radial servo control by an objective lens position detector 33, a radial servo control circuit 52, or a track driving device 32.
FUJIWARA KIYOSHI
UJIIE MASAHIKO
Shinji Kato