It was found that several hundred millivolts of d.c. voltage is generated in a metal-insulator-metal structured device of Langmuir-Blodgett (LB) films. The voltage generation is caused by LB films only or by a chemical reaction between LB films and the electrode. In the work reported in this paper, the experiments are processed for a sample which has been left under atmospheric conditions since its fabrication in 1986. We measured the same voltage as at the time of fabricating the LB films. The thickness of the LB films and the evaporated electrode used for the experiments is about 20 approximately 30 angstrom and 2000 angstrom respectively. Therefore, we cannot think that a chemical reaction which is generating several hundred millivolts takes place continuously for 6 approximately 7 years. It is proper that the chemical reaction has terminated. In our experimental results, the cause is some kind of e.m.f. which has occurred at elements of the film.