Abstract: A magneto-optical disc includes a pit forming region and a groove forming region on a surface of a substrate and a recording layer covering the pit and groove forming regions. The pit forming region includes a row of pits having a width of 0.40-0.55 .mu.m and a depth of 600-900 .ANG. and the groove forming region includes a spiral groove having a width of 0.95-1.15 .mu.m and a depth of 600-900 .ANG.. The disc is recorded and read by using an optical head with an objective lens having a numerical aperture of 0.40 to 0.50 and directing linearly polarized laser light having a wavelength of 600 to 900 nm to the disc such that its electric field vector has a direction perpendicular to the groove and the pit row. Tracking, seeking and information retrieval can be done with minimal errors using the same laser light beam in both the pit and groove forming regions.

Abstract: An optical disk substrate of resin, comprising a center hole and being composed of an inner circular-projected portion and an outer flat circumferential portion, the inner circular-projected portion having a circular projection projecting from at least one major surface of the substrate, the maximum height of the circular projection measured from the major surface of the outer flat circumferential portion being equal to or larger than 0.5 mm, the optical disk substrate is designed to satisfy the following equation or inequality:V/V.sub.0 <1.5, where V stands for the volume of the circular-projected portion, and V.sub.0 stands for the volume of an annular body having the same radius as the circular-projected portion and the same thickness as the outer flat circumferential portion, and having a center hole of the same size as the center hole.