A generator system, including first and second generators, a connection circuit connecting output lines of the first and second generators to each other and connecting neutral lines of the first and second generators to the ground, a switch command unit outputting commands to switch a connection mode of the first and second generators between parallel and series connection modes, a circuit switch switching a connection mode of the connection circuit in response to the commands, a data acquiring unit acquiring a waveform data of the first generator when the second generator is operated after the first generator is operated, and a control unit controlling the second generator to synchronize frequency and phase of waveforms of the first and second generators in the parallel connection mode and controlling the second generator to synchronize frequency and shift phase by 180 degree in the series connection mode.