A control unit repeats the series of processing of comparing a first phase representing a phase of the first reference sine wave and being a phase included in the first synchronization signal, with a second phase that is the phase of the second reference sine wave when the first synchronization signal is received when the communication unit receives the first synchronization signal from the other inverter generator, changing a phase change amount per unit time of the second reference sine wave in accordance with the comparison result, continuing to update the phase of the second reference sine wave so that the phase of the second reference sine wave changes with a phase change amount per unit time after the change with reference to the first phase until the next first synchronizing signal is received from the other inverter generator.