When the data is reproduced by irradiating a laser beam onto the optical disk, {HEAD ~ an amount} of {TAIL ~ irradiation beam detection signal} is produced according to the amount of the laser beam irradiated onto the optical disk, and the defect on the optical disk is detected on the basis of this amount of irradiation beam detection signal 
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When the data is reproduced by irradiating a laser beam onto the optical disk , { HEAD ~ an amount } of { TAIL ~ irradiation beam detection signal } is produced according to the amount of the laser beam irradiated onto the optical disk , and the defect on the optical disk is detected on the basis of this amount of irradiation beam detection signal
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH