PURPOSE: To decrease plane runout and warpage owing to a change in temp. and humidity and to obtain recording and reproduction with high quality on both inside and outside circumferences with an optical disk formed by superposing a substrate on which rugged grooves and rugged pits are formed and a protective plate by setting the weight difference between the substrate and the protective plate within apecific %.

CONSTITUTION: An optical disk is manufactured by setting the weight difference between substrates 1, 4 consisting of a polymethyl methacrylate (PMMA) having hygroscopicity as a resin within 10%. A layer 2 having rugged grooves and pit signal parts is provided on the surface of the body 1 by using a UV curing resin. A light-absorptive thin film 3 consisting principally of Tex, where 0<x<2.0, is formed on the layer 2. Said substrate 4 is superposed and joined on and to the film 3 of the lower plate 1 by using a UV curing resin 5 to form a protective plate. The warpage and shape change of the disk owing to a temp. and humidity fluctuation are decreased by regulating the weight difference between the plates 1 and 4 and in the above-mentioned way, by which the stability and the quality of the recording and reproducing signal are improved.