In the present invention, there is provided a battery pack wherein a lock recess for engagement with a lock protrusion formed to protrude from the battery mounting portion side and a detection groove for engagement with a detection protrusion formed to protrude from the battery mounting portion side so as to detect the kind of the battery pack are formed in one or each of mutually opposite side surfaces adjacent to a mount surface for mounting to the battery mounting portion, according to the kind of the battery pack, and the detection groove is formed to be deeper than the lock recess in a direction in the plane of the mount surface.