To provide an optical disk of which the address information start mark of a header area is accurately detected and to provide an optical disk device.
With respect to an optical disk 6, an address information start mark AM is recorded in the header area as a variable length code which is so encoded that the number of many second logical values between many first closest logical values may be 2 at least and 7 at most, and not only a first detection criterion but also a second detection criterion are adopted as detection criterions for the address information start mark AM. In the first detection criterion, the existence of a combination of pulse widths formed between the first logical values proves that the mark AM has been detected. In the second detection criterion, detection of the mark AM is proved by the fact that all the first logical values constituting the combination of pulse widths and the second logical values are correct at the time of inverting the logical value by the first logical values intermittently arranged between the second logical values.
TONE YASUO
SHIYUUDA YASUHIRO
