Terminal covers (51, 52) have terminal accommodation spaces, each of which has an opening of a predetermined shape that permits only one of battery terminals (24, 25), which is of predetermined polarity, to be fitted thereto. Each of the battery terminals (24, 25) is formed in such a manner as to have a predetermined shape enabling the battery terminal to be fitted into the corresponding terminal accommodation space. The battery body (27) has cover fitting holes (54a, 54b (55a, 55b)), which permit only fitting projection pieces (51c, 51d (52c, 52d))of the terminal cover (51 (52)) accommodating and holding the battery terminal (24 (25)) to be fitted thereinto, in the vicinity of the battery electrode (29 (30)) so that only the battery terminal (24 (25)) is placed at a fastening / fixing position on the battery electrode (29(30)) Each of the fitting projection pieces (51c, 51d (52x, 52d) ) is formed in such a way as to have a predetermined shape that permits these pieces can be fitted into the corresponding cover fitting holes (54a, 54b (55a, 55b)).