A battery pack comprises a battery core pack that has a plurality of battery cells held in a cell holder, and a case that accommodates the battery core pack. The case has an outer shell case that covers the side surface of the battery core pack, and a bottom case that covers the bottom surface of the battery core pack. A lower-side battery core pack frame that supports the battery core pack is secured in a lower-side securing groove provided to an inner wall of the outer shell case. The lower-side securing groove is disposed above the upper-end part of the bottom case attached to the lower-end part of the outer shell case.