Power supply device includes a plurality of secondary battery cells having a flat rectangular parallelepiped shape, a pair of end plates covering both end faces of battery stack having the plurality of secondary battery cells stacked on each other, and a plurality of fastening members for fastening end plates to each other. Each of the plurality of fastening members has a plate shape extending along the stacking direction of the plurality of secondary battery cells and is disposed on a corresponding one of opposite surfaces of battery stack. Through holes are formed in both ends of each plate shape. Each of the pair of end plates includes pipe portions inserted into the through holes of a pair of fastening members disposed on opposite surfaces of battery stack among the plurality of fastening members.