A dielectric layer is formed from an oxide containing Sn and at least one of Zn, Zr, Si and Ga. The molar percentages of Sn, Zn, Zr, Si, and Ga, relative to the total elements in the oxide, represented by a, b, c, d, and e, respectively, satisfy the conditions (1)-(7): (1) 0≤b/(a+b)≤0.6, (2) 0≤(c+d)/(a+b+c+d+e)≤0.5, (3) 0≤b≤50, (4) 0≤c≤40, (5) 0≤d≤45, (6) 0≤e≤40, and (7) 20≤b+c+d+e≤80. The dielectric layer enables favorable information recording in an oxide-based recording layer on which the dielectric layer is directly overlaid, does not require preventive measures for health hazard, and is superior in durability.