An optical disk 100 is provided with a hub 3 at the central portion of a substratel. A relationship Y/X0.015, preferably Y/X0.05 is satisfied where X is the projected area of the substrate 1 and Y is a contact area between the hub 3 and the substrate 1. As result, no slippage occurs between the hub 3 and the substrate 1 even when they are rotated at high speed than conventional. With this higher rotational speed, the data transfer rate is improved, and irregular rotation and the camming are suppressed, thereby reducing tracking errors and write/read errors.