the present invention relates to a high - density disk that is structured to prevent a collision of an optical pickup &# 39 ; s objective lens with the high - density disk if the disk is placed upside down in a disk device that is able to record and reproduce signals to / from the high - density disk . a high - density disk recording medium according to the present invention is structured such that , wherein a recording layer having high - density pit patterns is offset from a center plane of disk thickness , a center hole of the disk recording medium is asymmetric in shape with respect to the center plane where , for example , both entrances of the center hole have mutually different diameters .