Disk-shaped information recording medium, disk cartridge and information recording and reproducing apparatus

A information recording medium having a disk shape comprising:

• a substrate having a predetermined thickness;
• a first surface forming one surface of the substrate;
• a second surface forming the other surface of the substrate;
• a cylindrical portion in which a through hole penetrating a center of the substrate is formed;
• a first recording region formed on a first surface side;
• a second recording region formed on a second surface side;
• a first clamp region with which a clamper is brought into contact when the first recording region is reproduced, the first clamp region being formed on the first surface side;
• a second clamp region with which a clamper is brought into contact when the second recording region is reproduced, the second clamp region being formed on the second surface side;
• a first rib formed in a circular annular shape on the first surface side and on an inner peripheral side of the first clamp region;
• a second rib formed in a circular annular shape on a second surface side and on an inner peripheral side of the second clamp region;
• and
• a first printing region formed between the first rib and the first recording region.