ry data (f) to NRZ conversion. [0120]FIG. 5 is a schematic diagram of recording marks in multi-level recording. [0121]FIGS. 6A, 6B and 6C are a plan view, a sectional view of deformation without interference, and a sectional view of added deformation, respectively, of three recording marks formed in three successive cells mainly based on deformation and show linear interference in deformation. [01