Multi-layered phase-change optical recording medium

A multi-layered phase-change optical recording medium, comprising:

• a first substrate disposed at the front side as viewed from the laser beam irradiation side,
• a second substrate disposed at the innermost side as viewed from the laser beam irradiation side,
• each of the first substrate and the second substrate having a serpentine spiral guide groove on a recording surface side thereof,
• intermediate layers, and
• a plurality of information layers each having a phase-change recording layer, being disposed via each of the intermediate layers in between the first substrate and the second substrate,
• each of the information layers other than the information layer disposed at the innermost side as viewed from the first substrate side comprising the following five layers:
• an under protective layer,
• the phase-change recording layer,
• an upper protective layer,
• a semi-transparent reflective layer, and
• a thermal diffusion layer or a light transmissive layer, and
• the information layer disposed at the innermost side as viewed from the first substrate side comprising:
• an under protective layer,
• the phase-change recording layer,
• an upper protective layer, and
• a reflective layer,
• wherein each of the thermal diffusion layers or light transmissive layers of the respective information layers other than the information layer disposed at the innermost side as viewed from the first substrate side comprises an In oxide, a Zn oxide, an Sn oxide and an Si oxide, and when the contents of the In oxide, the Zn oxide, the Sn oxide and the Si oxide are represented by “a”, “b”, “c” and “d” [mol %] respectively, the following requirements are satisfied, and when the refractive index of the first and second substrates was represented by “n”, the laser light wavelength is represented by “λ” and the depth of the groove guide of the first and second substrates is represented by H, the depth of the groove guide H satisfies the following requirement,
• 3≦a≦50
• 0≦d≦30
• a+b+c+d=100
• λ/17n≦H≦λ/1.5n.