A first line includes a switching element and is electrically coupled to a branch point and an external load which is electrically connectable to a battery parallel-operation circuit. A second line includes a resistive element, and is electrically coupled to the external load and the branch point. The first line and the second line are each provided in a plurality. The plural first lines are connected in parallel to one another, and the plural second lines are connected in parallel to one another. The branch points are electrically coupled respectively to plural external, connectable battery units.