An inverter device, which has two operation modes including a grid-connected operation mode where the inverter device is interconnected with a commercial power system, and an isolated operation mode where the inverter device is independent of a commercial power system and performs an isolated operation, includes an inverter converting direct-current power received from a direct-current power supply of a solar battery array into alternating-current power, a control unit controlling an action of an inverter device, a plug for outputting the alternating-current power converted by the inverter, and a load-connecting receptacle on a path of a power supply line connecting the inverter and the plug, for outputting the alternating-current power.