A battery pack is loaded and unloaded to and from a battery mounting portion on the electronic apparatus side by sliding a housing thereof on the battery mounting portion. A lock recess is formed in each of side surfaces adjacent to a mount surface for mounting to the battery mounting portion through a pair of side edges parallel to the sliding direction of the mount surface, and a detection recess is formed in one or each of the side surfaces according to the kind of the battery pack; and the lock recess includes an inclined surface portion, and a clamped portion to be clamped between a bottom surface of the battery mounting portion and the lock protrusion, and the thickness of the clamped portion in a height direction is set to be larger than the depth of the detection recess in the same direction.