the eight patterns is quasi randomly selected per certain unit of recording 1 ecc block in this embodiment whenever rewriting is performed which corresponds to the recording mode of 6 described in the summary section as shown in fig6 as the result of the examination it turned out that jitter can keep less than 13 up to about 50 000 cycles and the effect of enhancing the rewrite performance is greater than the case where u201c the condition of selection is that the dsvs are equal u201d in the first embodiment this effect of enhancing the rewrite performance to a great extent is due to that intensive deterioration in fixed position on the disk was more suppressed setting the dsv threshold value at 10 as in the present embodiment did not give rise to deterioration in tracking performance and readback performance such as readback jitter however it turned out that setting the dsv threshold value greater causes a rise in readback jitter for example if the dsv threshold value is set at 100 readback jitter after 10 times of overwrite becomes 8 0 which exceeds an ideal initial jitter of 7 as we investigated what causes the jitter rise it turned out that cd components cannot be well suppressed when the dsv threshold value is greater than 10 and a slice level offset.