Patent ID: 8130628

Claim:
An optical recording medium having (N−1) (where N is a positive integer of 4 or more) information recording surfaces, wherein a cover layer formed between a surface of the optical recording medium where light is incident, and the first information recording surface closest to the medium surface; and first through (N−1)-th intermediate layers formed between the respective first through N-th information recording surfaces, the optical recording medium satisfying assuming that actual thicknesses of the cover layer and the first through the (N−1)-th intermediate layers of the optical recording medium having refractive indexes nr 1 , nr 2 , . . . , and nrN are respectively tr 1 , tr 2 , . . . , and trN in the order from the surface of the optical recording medium where light is incident, the thicknesses tr 1 , tr 2 , . . . , and trN are converted into thicknesses t 1 , t 2 , . . . , and tN of layers having a predetermined refractive index “no”, a defocus value with respect to a layer having a refractive index nrα and a thickness trα (satisfying: 1≦α≦N), and a defocus value with respect to a layer having the refractive index “no” and a thickness tα(satisfying: 1≦α≦N) are the same as each other, a difference DFF between the sum of a thickness “ti” through a thickness “tj”, and the sum of a thickness “tk” through a thickness “tm” is set to 1 μm or more (where i, j, k, and m are each any positive integer satisfying i≦j<k≦m≦N), and the thicknesses t 1 , t 2 , . . . , and tN are calculated by products of a function f(n) expressed by the following formula (4), and the thicknesses tr 1 , tr 2 , . . . , and trN: f ( n )=−1.088 n 3 +6.1027 n 2 −12.042 n+ 9.1007 (4) in the formula (4), n=nr 1 , nr 2 , . . . , and nrN.