The purpose of the present invention is to provide a power source which can avoid short-circuiting of neighboring cells. This power source (1) is provided with multiple cells (22) comprising positive electrodes (20) and negative electrodes (21) disposed in alternately opposite directions, multiple busbars (3) arranged on a line so as to connect multiple cells in series, and a sheet-form insulating film (5) which is arranged on at least one side of the busbars; this power source (1) is further provided with a resin frame which fixes the multiple cells, and insulating parts (29, 29A) are provided on the insulating film or the resin frame (23) to insulate the neighboring cells on the side of neighboring busbars.