A battery pack includes a circuit board disposed on the inner side of a mount surface to be mounted to a battery mounting portion, and a terminal portion at one surface adjacent to the mount surface. The battery pack is mounted into the battery mounting portion by sliding the mount surface on the battery mounting portion. A recess is formed at one or each of a pair of edge portions which are formed between the mount surface and both side surfaces adjacent to the mount surface through a pair of side edges parallel to the direction of sliding of the mount surface in the battery mounting portion, according to the kind of the battery pack.