To prevent deterioration of battery performance, breakage owing to electrolyte leakage, or a danger of damaging a human body, when short- circuiting happens between output terminals due to external factors such as contact with a metal fragment because the output terminals are positioned on a surface of a pack, in the case of a cassette-type battery pack using a set of batteries of Ni-Cd, Ni-MH, or the like.

A switch 3 is provided between a set of batteries 6 and an output terminal 2. During insertion into an electronic apparatus, the switch 3 conducts causing the electronic apparatus to be powered, and during extraction from the electronic apparatus, the switch 3 is opened and the output terminals 2 are not electrified, and therefore the set of batteries 6 are protected from short-circuiting due to short-circuiting of the output terminals 2.