According to an embodiment, a voltage fluctuation suppressing apparatus is provided with a power storage device connected to an electric power system, a basic control unit to control an output of the power storage device, a voltage detector to measure a voltage of a connection point to the electric power system, and an output control unit to divide a control amount to be outputted to the basic control unit into a reactive power command value and an active power command value and to output them. The output control unit is provided with a reactive power upper limit value calculation unit, a reactive power calculation/output unit, and an active power calculation/output unit.