The power-supply device includes: a battery assembly composed of a plurality of batteries each having a positive electrode end and a negative electrode end, said batteries overlapped with each other in a manner that electrodes having the different polarities are adjacent to each other; a plurality of bus bars connecting the batteries in series by connecting the adjacent electrodes having the different polarities in the battery assembly; and a terminal having an electric contact part attached to each bus bar, and a wire connecting part continued to the electric contact part, and attached to an electric wire connected to a voltage measuring device for measuring a voltage of the battery. The electric contact part includes a pair of clipping pieces disposed with a gap from each other, and connected to the bus bar by press-inserting the bus bar into between the clipping pieces.