In an inverter generator controller, residual charge of a battery is detected and generated power output is detected. Then, low-load charging of the battery is implemented if the detected generated power output of the engine generator unit is equal to or greater than the detected load output demand and the detected generated power output of the engine generator unit is less than the predetermined low-load value a, when the detected residual charge of the battery is equal to or less than the first threshold value. When the detected residual charge of the battery becomes greater than the first threshold value, the low-load charging of the battery is terminated.