A power source apparatus includes first equalizing circuits to control remaining charge capacity variation among a plurality of battery units, and second equalizing circuits to control remaining charge capacity variation among all the series-connected battery packs that make up each battery unit. A first equalizing circuit connects each battery unit with an output line OL through a first series circuit made up of a first limiting resistor and first equalizing switch. Remaining charge capacity variation is equalized among all the battery units by the first equalizing circuits, and remaining charge capacity variation between battery packs in each battery unit is controlled by the second equalizing circuits.