A method and apparatus for the decontamination of fluid ammonia are described. The video document is decomposed into scenes, shots and frames, and an importance value is assigned to each scene, shot and frame. If a change is made in the evaluation result by making transition from the second evaluation mode to the first evaluation mode, the user sensuously recognizes again that the finger placement is not proper from the evaluation result and is prompted to perform a correct operation of the finger position.