The present invention relates to optical disks and optical disk devices, and has an object to reduce access time and prevent malfunction. To attain the above object, in an optical disk (100), a management information area (130) is placed inside a user data area (140), namely, at the innermost circumference position of the optical disk (100), in an information layer (101) placed at the farthest position from the surface. A position information area (132) that stores position information indicating the position of each information layer in a thickness direction of the optical disk (100) is placed in the management information area (130).