An absolute time area is expanded by using an area of relatively low
importance such as zero-data area and/or relative time area or the like in
a Q channel in a sub-code in a recording format of a CD. Thus, an absolute
time expression which can cope with a disc having a large capacity or the
like can be performed. An absolute time expression is performed in a
manner such that a digit of "100 minutes" is BCD expressed by using lower
4 bits in the 8-bit zero-data area ZERO. Thus, the absolute time of up to
999min59sec74frame can be expressed. A digit of "hour" is also expressed
by using the lower 4 bits in the zero-data area. For example,
identification information showing that a disc is a high density optical
disc of large capacity is expressed by using the upper 4 bits in the
zero-data area ZERO.
