On a recording layer (12) of a disc-shaped optical recording medium (10), a plurality of virtual recording cells (40) are assumed contiguously in a spiral or concentric fashion in a groove (16). The irradiation time of the laser beam is modulated in five stages or more for each of the virtual recording cells (40) in response to information to be recorded, thereby forming recording marks (48A to 48G) of different sizes in five stages or more. The optical reflectivity of the virtual recording cell (40) is modulated in multi-stages to thereby vary the reflection level of a reading laser beam for reading operations in five stages or more. The length of the virtual recording cells (40) in the rotational direction of the disc is set to be equal to that of an arc having the same center angle with respect to the center of the disc.