| 摘要 |
PROBLEM TO BE SOLVED: To surely discriminate a different kind of disk by detecting the presence of a reflecting layer in the same specific position in the diametral direction of each of plural different kinds of disks and discriminating the kinds of disks based on this detecting signal. SOLUTION: The 1st disk 12 is an optical disk having its substrate 1.2mm thick, and the 2nd disk 13 is an optical disk having its substrate formed by sticking two substrates, each measuring 0.6mm in thickness to each other. In the optical disk 12, an outer circumferential part of its reflecting layer 4 is formed to the extend toϕ118 out ofϕ120. On the other hand, in the optical disk 13, both outer circumferential parts of its reflecting layers 9 are formed to the extend up toϕ120. A light emitting part 14 and a light receiving part 15 are arranged in a holder 16 at an end part of each of the optical disks 12 and 13 respectively. In the case of the optical disk 12, a light beam 17 emitted from the light emitting part 14 is passed through a transparent substrate 2 and a protective layer 5. On the other hand, in the case of the optical disk 13, a light beam 17 emitted from the light emitting part 14 is reflected by the reflecting layer 9 to arrive in the light receiving part 15. Consequently, the optical disks can be discriminated.
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