An optical reproducing device is provided with predetermined length mark signal measurement means which measures amplitude values of a 2T mark and an 8T mark, which are a short reproducing power control mark and a long reproducing power control marks, respectively, from information data recorded in an magneto-optical disk. The elongated housing defines a generant bed. The implant provides bilateral support of the adjacent vertebrae when inserted into the disc space from a postero-lateral approach. In some embodiments the work surface may be movable relative to the container, whether slidable in a co-planar or parallel planar manner in translation, or folding as in a foldable shelf.