A metal plate and an electrode in a polymer lithium ion secondary battery or the like are welded certainly, and it is accomplished to further improve the reliability and the durability thereof. Each of an upper metal plate (7a) and a lower metal plate (9a) on the positive pole/terminal is welded to a pole/terminal of positive electrode (3) so that the pole/terminal of positive electrode (3) may be sandwiched from each of the upper and lower sides. Moreover, each of an upper metal plate (7b) and a lower metal plate (9b) on the negative pole/terminal is welded to a pole/terminal of negative electrode (5) so that the pole/terminal of negative electrode (5) may be sandwiched from each of the upper and lower sides. This eliminates occurrence of poor welding in the electric resistance welding.