In addition, when {HEAD ~ the data} is reproduced by irradiating {TAIL ~ the laser beam} onto the optical disk, the amount of irradiation beam detection signal is produced according to the amount of the laser beam irradiated onto the optical disk, an amount of reflected beam detection signal is produced in accordance with the amount of the laser beam reflected from the optical disk, and the defect on the optical disk is detected on the basis of the amount of irradiation beam detection signal and the amount of reflected beam detection signal 
In addition , when { HEAD ~ the data } is reproduced by irradiating { TAIL ~ the laser beam } onto the optical disk , the amount of irradiation beam detection signal is produced according to the amount of the laser beam irradiated onto the optical disk , an amount of reflected beam detection signal is produced in accordance with the amount of the laser beam reflected from the optical disk , and the defect on the optical disk is detected on the basis of the amount of irradiation beam detection signal and the amount of reflected beam detection signal
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL 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 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 OTH OTH OTH OTH OTH OTH OTH OTH