To surely prevent reverse connection of batteries by forming a contact prevention part preventing the contact therewith, when the other terminal faces to a battery contact piece in contact with one terminal of a cylindrical battery.

A contact prevention part preventing the contact a bottom part by contacting with an insulating part 81c of a battery 81 is constituted of a tip part 85d1 and a recess part 85d2 of a battery contact part 85d. When the battery 81 is so installed that a positive terminal, or one terminal contacts a battery contact piece 85, the positive terminal enters the recess part 85d2 of the battery contact piece 85 and contacts to enable conduction. On the other hand, when a negative terminal 81b, or the other terminal is installed to face to the battery contact piece 85, the insulating part 81c formed in the circumference of the negative terminal 81b contacts with the tip part 85d1 of the battery contact piece 85 and prevents the negative terminal 81b from contacting so as to make the conduction impossible. The battery contact piece 85 is so formed to contact the battery with its large-diameter end side and may comprise a volute spring, which is so constituted that a part of the spring passes the center of the end.