A converter which converts first AC power input from an external power system to DC power, a storage device charged with the DC power from the converter, an inverter which converts DC power from the storage device to second AC power, an output AC power generating unit to which the first AC power and the second AC power are input, the unit which generates output AC power, and a controller which obtains external power information indicating a relationship between a power supply and a power demand in the external power system through a network and outputs a control signal to control the output AC power generating unit according to the external power information are provided. The controller controls the output AC power generating unit according to a state of a margin of the power supply.