An optical disc comprising a substrate and a recording layer and a light-transmitting layer, laid on a substrate one upon the other in the order mentioned. The pre-stage gear is released after the torque transfer is completed with the electric motor, and the clutch is exchanged after synchronizing the motor speed with the electric motor. Content are divided into a plurality of working periods. Each surface section occupies one-third of the hole length. In preferred embodiments, the marking is formed in a photosensitive coating that is applied to the optical media, and then cured with a first light. Used, as a sensor portion, are compound materials such as FeN showing a significant anomalous Hall effect, and materials containing magnetic properties such as a magnetic semiconductor having a zincblende structure and oxide having a perovskite structure.