PURPOSE: To provide a system capable of writing, reading, and erasing in a high density and at a high speed and further capable of erasing many times by using an optical disk coated with a electron trapping medium.

CONSTITUTION: A middle layer 14, an electron trapping layer 16, a protection layer 18, and a coating layer 19 are sequentially formed on a disk substrate 12. A writing laser beam 28 generates a visible beam of light which has a peak in a wave length of about 460nm and is emitted onto a disk 10 through a head 32. The irradiation of this visible beam of light excites carriers, which are filled in a trapping place and recorded as information. Reading is done by irradiating the disk 10 with a beam of infrared from a reading focus laser 38 through the head 32 to emit photon from the trapping place. The emitted photon is detected by the head 32 and is processed with optical system 31 before being outputted through a detector device 40. This configuration enables writing, reading, and erasing many times in a high density and at a high speed.