An optical disk comprises a polycarbonate substrate, a first protective layer formed on the substrate and made of SiO.sub.2, a recording layer formed on the first protective layer and made of an In-Sb-Te alloy, a second protective layer formed on the recording layer and made of SiO.sub.2, and a surface protective layer formed on the second protective layer and made of an ultraviolet curable resin. The recording layer has a composition of In.sub.50-x Sb.sub.50 Te.sub.x (wherein x is in atomic % and falls within the range of 0