PURPOSE: To improve recording density, the amount of information and reading speed while obtaining information corresponding to the ratio of interference between incident light and emissive light to one pit by changing the height of an uneven part in the pit.

CONSTITUTION: With the upper face of a substrate 51 as a reference, the heights of four pits 521, 522, 523 and 524 are defined as h1, h2, h3 and h4 and the wavelength of a laser is defined as λ. At such a time, conditions are established as follows; h1=λ/4, h2=2/3h1, h3=1/2h1 and h4=1/3h1. Light path difference (d) between the case of reflecting a laser beam on the upper face of a pit 52 and the case of reflecting the laser beam on the upper face of the substrate 51 is made double as much as the height of the pit. On the other hand, phase difference is made 2π/λ fold as much as the light path difference (d), and by adjusting the spot of a light source so that the intensity of light to be reflected on the upper face of the pit and the intensity of light to be reflected on the upper face of the substrate can be equal to I0, the intensity of light in each pit is like shown in a graph. This intensity of light is outputted as the pit information having five stages.