A power supply device includes a battery block formed by stacking a plurality of battery cells in a thickness with separator interposed between corresponding battery cells, a pair of end plates disposed on respective end faces of the battery block, and a binding bar coupled to the pair of end plates to fix the battery block in a compressed state together with the end plates. Separator includes heat-insulating sheet and elastic layer layered on a surface of heat-insulating sheet, elastic layer having elastic protrusion that is partially in adhesion to a case surface of battery cell and is deformed by expansion of battery cell, and deformation space is provided for elastic protrusion pressed by battery cell to be displaced in an outer peripheral direction orthogonal to a pressing direction.