This paper studied effects of yen appreciation on the Japanese economy and changes in energy demand when assuming the medium-term yen appreciation trend, and subjects in the energy industry. The paper also refers to the trend of the Asian material industry largely influencing the energy supply/demand, the risk hedge problem of the exchange, and international cooperation and business development of the energy industry. The energy industry is extremely high in public interest and is rice of the industry. Therefore, the development of the business has focused on the domestic market. However, such a recognition is forced to be changed by waves of the worldwide deregulation. Discussions on foreign/domestic price differences caused by high yen and a series of deregulation policy in the energy industry affected thereby may be concrete signs. The subject in the energy industry under the yen appreciation is that the energy industry will be close to common sense in general industrial circles and change to an industry which is strong and internationally competitive enough to brave the exchange variation. 101 refs., 104 figs., 31 tabs.