Patent ID: 7228554

Claim:
A driving unit for executing recording/reproducing to a recording disk, comprising in a disk holding portion for holding the recording disk: a first centering member having a predetermined outer diameter; a second centering member having an outer diameter smaller than that of the first centering member; and a protrusion size changing mechanism for changing a protrusion size of the second centering member toward the recording disk with respect to the first centering member, wherein when the recording disk held by the disk holding portion has a center hole of a predetermined diameter formed in the center portion of the recording disk, and a centering hole formed in the hub fixed to the recording disk, the centering hole having a diameter smaller than that of the center hole, the disk holding portion centers the recording disk by coupling the second centering member into the centering hole, wherein: the second centering member is capable of having a portion thereof inserted into the recording disk; the protrusion size is the size of the portion of the second centering member that is inserted into the recording disk; and the protrusion size changing mechanism changes the size of the portion of the second centering member that is inserted into the recording disk by retreating the first centering member with respect to the second centering member.