NOVELTY - Power supply device includes pair of end spacers (17) that covers end battery cells (1) among the battery cells located on end sides of battery block, which comprises battery cells and separators (2a-2d) that are alternately arranged side by side. Each of the end spacers forms hollow thermally-insulating layer(s) (18) that is located on a side of the end spacer in contact with the end battery cell.    USE - Power supply device e.g. for electric vehicles or plug-in hybrid vehicles, such as hybrid car.    ADVANTAGE - The device can reduce temperature difference among battery cells and maximize the performance of the battery cells. Since the end plates are made of metal, mechanical coupling force by the end plates can be improved, and the thermal conductivity of the end plates can be high. Thermally-insulating layers, which define the closed chamber, can prevent that a battery cell that faces the end plate is cooled at higher cooling performance than other battery cells. Thus, it is possible to improve the mechanical strength of the power supply device, and to uniformly cool the battery cells. The end spacer can be formed only by closing the ends of the cooling gap. Thus, the separator and the end spacer can be manufactured at low cost. Thermally-insulating layer with the same width as the cooling gap can be easily formed. The battery cell that faces the end spacer can be cooled, but the flow rate of cooling gas in the cell is suppressed as compared with other battery cells. Thus, the cooling performance balance can be achieved. The number of cooling gaps is gradually increased from the end side of the battery block, or the number of the thermally-insulating layers of the separator is gradually reduced. Thus, the cooling performance is gradually reduced for cooling battery cells that are likely to obtain cooled more effectively toward the end surface. As a result, the temperature of the battery cell on the end side is relatively increased. Thus, it is possible to even the temperatures of the battery cells as a whole.    DETAILED DESCRIPTION - Power supply device comprises rectangular battery cells (1); separators (2a-2d) that are made of resin, each of the separators being interposed between the battery cells and in thermal contact with the surfaces of adjacent battery cells among the battery cells, and electrically insulating the adjacent battery cells from each other; pair of end spacers (17) that cover end battery cells among the battery cells located on the end sides of battery block, which comprises battery cells and separators that are alternately arranged side by side; pair of metal end plates (10) that cover surfaces of the end spacers and are thicker than the end spacers; and coupling components that couple the pair of end plates to each other, where each of the separators forms cooling gaps on the sides in contact with the adjacent battery cells, and cooling gas flows through the cooling gaps. Each of the end spacers forms hollow thermally-insulating layer(s) (18) that is located on a side of the end spacer in contact with the end battery cell.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional view showing the battery block.    Battery cells (1)    Separators (2a-2d)    Metal end plates (10)    End spacers (17)    Hollow thermally-insulating layer (18)