A battery pack disclosed herein includes a plurality of arranged battery cells and a battery holder configured to hold the battery cells. The battery holder includes a planar portion extending along a broad width surface of each of the battery cells and a protruding portion provided at each of both ends of the planar portion and protruding from the broad width surface. The protruding portion includes two recessed portions each being configured such that a corresponding one of side portions provided at both ends of the broad width surface fits therein.