When we recognize “learning” as a result of educational service, we should take more care for providing more suitable learning circumstances, especially in case of the education for the sustainable development, adequate circumstances may be more important, such as the way of preparing the nature as a learning material. In this study we tried to quantify the appropriate learning environment using the term of stress. Because the best performance could be obtained under some adequate stresses and arousal shown by the Yerkes-Dodson's law, therefore, we assumed that the relationship between stress and performance could be applied for extending the learning efficiency. From this point of view, stress was measured using activity of salivary amylase when students were enrolled in a lecture. Stresses were measured 4times during the lecture. We were able to consider about problem of the lecture from stresses of the students measured.