To properly control the dispersion of capacity of battery blocks.

A voltage measuring part 120 measures the terminal voltage periodically via a potential detecting line L which is connected electrically to both terminals of each battery block B, and a discharge part 110 performs discharge separately for each battery block by electrically connecting both ends of a discharge element Rc to both terminals of a battery block via the potential detecting line L. A discharge controller 130 periodically computes the quantity of dispersion of electromotive force among the battery blocks, based on each measured terminal voltage, in parallel with the measurement of each terminal voltage by the voltage measuring part 120, and orders the discharge part 110 to discharge the battery block highest in electromotive force, in case that the quantity of dispersion is over the first reference quantity. Furthermore, the discharge controller 130 orders the discharge part 110 to stop the discharge to the battery block during discharge before the measurement is performed, in case that the voltage measuring part 120 measures the terminal voltage of the battery block during discharge by the discharge part 110.