A disk unit wherein a disk is inserted by a plurality of arms, the arms being able to convey two types of disks different in diameter while supporting an outer periphery edge of each of the disks. A disk is loaded to the interior of the disk unit by automatic loading, and a disk accommodated in the interior of the disk unit is unloaded to the exterior of the disk unit. The disk unit comprises a limit switch, the limit switch being actuated by an arm that is pressed by an outer periphery edge of a large diameter disk or a small diameter disk upon insertion of the disk from a slot of a bezel. The insertion of the large diameter disk or the small diameter disk is determined on the basis of the state of operation of the limit switch.