The power conditioner determines possible total power and working individual power to be in a range that possible individual power of each of the power supply units is not exceeded. The possible total power is determined from the possible individual power, of each of the power supply units, determined based on the battery information detected by each of the unit controllers, collected by a master controller from each of the unit controllers. The working individual power is determined based on a power deviation indicating a difference of charging and discharging power between the power supply units. The power conditioner causes charging and discharging of each of the power supply units within the calculated working individual power.