Power supply device includes: battery stack in which a plurality of battery cells each having electrode terminal formed on a top surface thereof are stacked; a pair of end plates respectively covering end surfaces in a stacking direction of battery stack; fastening member that fastens the pair of end plates to each other; and insulating member interposed between a side surface of battery stack and fastening member. Insulating member has groove extending in a stacking direction of battery stack on a surface facing battery stack.