A new type of twin-roller(soft-roller) for rapid-quenching was developed, which is most suitable for producing amorphous and crystalline films of brittle materials such as ceramics, metals and alloys. By the use of this apparatus, amorphous and crystalline films of KNbO3 composition were prepared, which are not only very thin (50–100 µm), wide and long, but also of enough good quality for measuring electrical properties. Amorphous-ceramics and sintered bodies of the system were characterized by X-ray. Their electrical properties such as dielectric, ferroelectric and pyroelectric ones were measured, so that these results suggest a possibility of applying the crystallized films to a pyroelectric detector.