A power supply device comprising: a magneto generator including a rotor including a magnet forming a magnetic field; a rectifying unit rectifying an alternating current of the generator to a direct current and supplying to an electrical load; a voltage detection unit detecting a voltage of the electrical load; an opening unit interrupting electrical conduction of an output of the generator; short-circuiting units electrically short-circuiting the output; a torque supplying device supplying torque to the rotor; a voltage control unit selectively performing one of opening-control of controlling on/off switching of the opening unit and short-circuit-control of controlling on/off switching of the short-circuiting units to control the voltage of the electrical load to a predetermined value in accordance with the voltage detected by the voltage detection unit; a switching control unit switching and controlling between the above two controls in accordance with an operating state regarding rotation of the rotor.