PURPOSE: To obtain an electrooptic device which is dense and has a high degree of electric insulation and large capacitance by treating a Ta thin film formed on at least one of two substrates by anodic oxidation to form a transparent insulator, and to provide the electric capacity.

CONSTITUTION: The 1st metal 8 is formed on a substrate 7, and patterned in a specific shape and then the surface of the metal 8 is oxidized to form an insulator 11; and the 2nd metal 12 is then formed and patterned in a specified shape. The Ta thin film 13 is formed after an unnecessary part 12 is removed from the insulator 11. Then, this film is anod-oxidized to produce Ta2O5, which is a transparent insulator. The obtained Ta2O5 film has no pinhole and is dense and a high degree of insulation is obtained to avoid the application of a DC voltage to a liquid crystal layer. Further, crystallization is scarce and even if a minute crystallization is caused, no damage such as cracking is effected. The dielectric constant of Ta2O5 is six times that of SiO2, so the capacity of the transparent insulator is increased by six times without increasing the thickness.