PURPOSE: To improve adhesion strength of a thin magnetic film onto a plastic substrate by forming the thin magnetic film via an intermediate glass layer for vapor deposition on the plastic substrate.

CONSTITUTION: A glass layer 2 having 1,000 A thickness is formed on a transparent polymethyl methacrylate substrate 1 having, for example, 12cm diameter and 0.12cm thickness by using a vacuum deposition device and glass for vapor deposition consisting of 84wt% SiO2, 10wt% B2O3, 3wt% Al2O3 and wt% Na2O wt% and performing vapor deposition for 5min under the conditions of the substrate temp. of a room temp. and 6W10×10-6Torr degree of vacuum. The vapor deposition is thereafter performed for 3min by a two-element vapor deposition method under the conditions of the substrate temp. of a room temp. and 3×10-6 Torr degree of vacuum to form a thin Tb-Fe magnetic film 3 having 5,000 A thickness on the layer 2. A thin SiO2 film having 2,000 A thickness is then deposited by evaporation on said film for the purpose of protection.