A power source device includes: a battery assembly including a plurality of battery cells which are aligned; a bus bar module formed by linking a plurality of bus bar storing portions which store a plurality of bus bars which link and connect electrodes of the battery assembly; a smoke exhausting duct provided on one side of the battery assembly; and a control board provided on the smoke exhausting duct and electrically connected to a voltage detection terminal for detecting a voltage of each of the battery cells. In the smoke exhausting duct, a portion where the control board is provided is in a flattened shape having a smaller height and a larger width in comparison with another portion.