A power supply device, which is simply assembled and in which a cell assembly and a measuring section are freely inserted and detached, is provided. A power supply device 1 includes a cell assembly 2, a plurality of first bus bars 51, a plate 3 to which the plurality of bus bars 51 are attached. The plate is overlapped on the cell assembly 2. The cell assembly 2 has a plurality of cells 21 respectively including positive electrodes 23 at one ends and negative electrodes 24 at the other ends. The first bus bars 51 connect the positive electrodes 23 of the one cells 21 to the negative electrodes 24 of the other cells 21 of the cell assembly 2 which are mutually adjacent when the plate 3 is overlapped or overlaid on the cell assembly 2. The power supply device 1 includes a positioning unit 71 that relatively positions the cell assembly 2 to the plate 3 and a guide unit 72 that guides the plurality of first bus bars 51 to positions where the first bus bars 51 connect the respectively corresponding positive electrodes 23 to the negative electrodes 24 when the plate 3 is attached to the cell assembly 2.