"Moreover, the distance between the outer circumferential edge of the intermediate area 83 and the outer circumferential edge of the second recording layer 64 may be adjusted in range of 0.3 mm or more but not exceeding 0.6 mm.Moreover, the groove 31 and the position determination pits 33 in FIG. 7 are a specific example of the first concave portion, and the groove 34 and the overrun prevention pit" . . . .