A disk with an Ag reflective layer, a recording layer including elements Sb and Te, and a dielectric layer including S provided between the reflective layer and the recording layer has the problems of corrosion of the Ag reflective layer, decline of the signal quality due to insufficient heat releasing ability, and exfoliation between the layers. (1) A phase-change optical disk includes, on a transparent substrate, a recording layer in which an optically detectable reversible change between an amorphous phase and a crystalline phase can be caused by irradiation with an energy beam, a reflective layer, and a dielectric layer arranged between the recording layer and the reflective layer, wherein the main component of the dielectric layer is an oxide or a nitrooxide of Ta. (2) Between the recording layer and the dielectric layer, a layer including a nitride, an oxide, a carbide or nitrooxide of an element .alpha. (wherein .alpha. is at least one element selected from Sn, In, Zr, Si, Cr, Al, V, Nb, Mo, W, Ti, Mg and Ge) is provided.