To provide an information recording disk which detains a hub in a loose fitting state and is narrowed in the spacing from a recording surface to a disk reference plane.

A substrate 1 has a recessed part 3 housing the hub 2 in a the loose fitting state in its central part. An inner peripheral wall 3a of the recessed part 3 in which the hub 2 is housed is projected from the recording surface 6 in the rotating axis direction of the disk, by which an annular rib 4 is formed. The position of the hub 3 in the radial direction of the disk is regulated by the inner peripheral wall 3a of the recessed part 3. The position of the hub 2 in the rotating axis direction is regulated by the inside wall of an upper cartridge 31. The information recording disk produced by using such substrate may be made narrower in the spacing from the disk reference plane 8 to the recording surface 6 than heretofore. Further, the cartridge for housing such information recording disk may be formed thinner.