A DVD-R 1 has a main information area 2 where data information is recorded in a track having a wobble, and first and second control data areas 3,15 each of which is disposed in an inner space closer to the disk center than the main information area 2. The timestamp associated with each log entry is monitored with respect to an expiration value so that expired log entries may be identified. The amplifier includes plural amplification stages, a limiter, a tunable narrow band filter and a microcontroller. Freedom of the assembly order is therefore increased.