The inverter generator controller equipped with the engine generator unit driven by the engine and operates to prompt user to specify the load to be used (S10); to respond to load specified by user in response to prompt by selecting and connect to the engine generator unit at least one among multiple batteries differing in discharge capacity per unit time (S12 to S22); and to control charge/discharge of the connected battery/batteries and operation of the engine generator unit based on load output demand from the specified load (S24).