There is provided a charge/discharge determining apparatus for managing a natural energy power generation facility, a power plant and a plurality of batteries in an electrical power system. The apparatus includes: a system information acquiring section configured to acquire an actual value of natural energy power that is supplied from the natural energy power generation facility to the electrical power system; a battery information acquiring section configured to acquire battery electric energy information from the respective batteries, wherein the battery electric energy information indicates charge/discharge electric energies of the respective batteries which can be discharged from or charged in the respective batteries; and a determining section configured to determine at least one battery to be charged/discharged from among the plurality of batteries, wherein when an absolute value of a difference between the actual value and a predicted value of the natural energy power is larger than a threshold value.