Power supply device and vehicle provided with power supply device

A power supply device comprising:

• a plurality of battery cells each having a thickness thinner than widths of principal surfaces, and having a rectangular outer shape;
• separators each interposed between the battery cells and insulating mutually adjacent ones of the battery cells from each other, in a state that the plurality of battery cells are stacked with the principal surfaces facing each other;
• and
• a fastening member for fastening a battery cell stack including the battery cells and the separators alternately stacked on each other,
• wherein each of the separators includes
• a sandwiching plate portion disposed between the facing principal surfaces of the mutually adjacent battery cells, and
• a plate-like bottom-surface cover portion provided to both surfaces of the sandwiching plate portion, at a lower end of the sandwiching plate portion, and protruding in a stacked direction of the battery cells to cover bottom surfaces of the battery cells, and
• the bottom-surface cover portions of the separators stacked on both surfaces of the battery cells are stacked on each other at the bottom surfaces of the battery cells.