In an inverter generator having a first, second and third inverters, a first, second and third controllers adapted to control turning ON/OFF of switching elements thereof and to operate the first inverter as a master inverter and the second and third inverters as slave inverters, a three-phase output terminal, a single-phase output terminal, and an engine control section adapted to send an output of a selector switch to the first controller and so on, thereby outputting three-phase or single-phase AC through control of turning ON/OFF of the switching elements, so that the outputs from the first, second and third inverters become in the three-phase or single-phase AC in response to the output of the selector switch making the output from the first inverter as a reference.