POWER SUPPLY DEVICE, ELECTRIC VEHICLE AND POWER STORAGE DEVICE PROVIDED WITH SAID POWER SUPPLY DEVICE, AND FASTENING MEMBER FOR POWER SUPPLY DEVICE

A power supply device includes a battery stack body including a plurality of secondary battery cells are stacked, a pair of end plates covering both end surfaces of the battery stack body, and a plurality of fastening members each disposed on an opposing side surface of the battery stack body to fasten the end plates to each other. Fastening member includes end-part fastening parts fixed to the end plates at both ends in a longer direction, and intermediate coupling part coupling end-part fastening parts to each other, and intermediate coupling part has a plate shape extending along a side surface of the battery stack body, and includes a plurality of rows of coupling bars formed in a wave shape in front view of fastening member. At the time of expansion of the secondary battery cells, the power supply device elastically deforms coupling bar in a plane along the side surface of the battery stack body so that intermediate coupling part stretches in the stack direction of the secondary battery cells.