In the power supply device, there is a problem that it is difficult to attach the cover member when the length of the bus bar module connecting the battery varies. The present invention aims to solve the above-mentioned problems by a method in which, as opposed to a battery assembly in which a plurality of batteries are stacked has a plurality of bus bars connecting adjacent batteries to each other, the bus bar is mounted and stacked on the battery. The main body part (8) on the assembly, the bus bar module (6) with a plurality of positioning protrusions (29) and a plurality of locking parts (30) arranged on the main body part, the above-mentioned cover part (1) has multiple The stacking direction (X) of each battery is arranged in a row, and covers a plurality of covering parts (10) of each bus bar, and an elastic deformation part (14) that displaceably connects the adjacent covering parts to each other, and the covering parts respectively have The positioning hole (11) through which the above-mentioned positioning protrusion is inserted, and the locking receiving part (12) which is locked by the above-mentioned locking part. A shape that can be inserted.