A disk drive including a tray having a seating portion in which a disk or disk cartridge is seated, and an opening hole, and further having a disk cartridge holder installed on the tray to be capable of sliding, the disk cartridge holder fixing the disk cartridge to the seating portion. The disk cartridge holder includes a plurality of ribs which protrude toward the opening hole and which prevent the disk, to be seated in the seating portion, from becoming caught between the disk cartridge holder and the tray.