A generation device, having a magneto generator, in which an AC control voltage is applied from a battery charged with a rectified output of the magneto generator to an armature winding of the generator through an inverter to control a battery voltage to a limit value or less, comprising: fixed point detection means for detecting a fixed point on a waveform of a phase current of the generator; phase current phase detection means for detecting a phase angle of the fixed point in relation to a reference phase; arithmetical operation means for arithmetically operating timing for generating the AC control voltage with reference to the phase of the fixed point; and inverter control means for controlling switch elements of the inverter so as to generate the AC control voltage at the timing arithmetically operated by the arithmetical operation means.