POWER SUPPLY DEVICE

The power supply device includes a plurality of battery cells each having a rectangular outer shape, a plurality of separators configured to insulate adjacent battery cells, and a restraining member assembling the plurality of battery cells and the plurality of separators. Each of separators includes interposed plate disposed between adjacent battery cells, heat insulating member having a sheet-like shape and disposed between interposed plate and adjacent battery cells, peripheral wall protruding from interposed plate toward adjacent battery cells and defining a housing space housing adjacent battery cells, and a plurality of ribs provided inside peripheral wall. The plurality of ribs holds heat insulating member.