An energy storage apparatus includes: a battery system including at least one battery; a power converting unit converting input/output power characteristics of the battery system into alternating current (AC)-direct current (DC) or DC-AC; a conversion control unit controlling an operation of the power converting unit; an initial driving unit converting DC power of the battery system into AC power and supplying the AC power as power for activating the conversion control unit; and a power selecting unit detecting an output voltage of the power converting unit, selecting, based on a level of the output voltage of the power converting unit, any one of AC power output by the initial driving unit and AC power output by the power converting unit, and supplying the selected AC power as operation power of the conversion control unit.