To obtain a ferroelectric thin film which is excellent in electro-optic characteristics and more particularly secondary electro-optic coefficients in spite of a deposition method using a solution.

The surface of a substrate is spin coated with an organic metal decomposition (MOD) solution raw material by using, for example, an MOD process and the coating is dried, by which the dry film is formed. The dry film is thereafter subjected to firing to form the ferroelectric thin film from the dry film. In succession, the thin film is cooled in such a manner that the cooling temperature gradient after the firing attains 1 to 15°C/second.