A power source is disclosed. The power source includes a first power source applying a first voltage to a control unit and a second power source applying a second voltage to a unit controlled by the control unit. The power source includes a first power supplying unit, which includes a main power switch and a first relay and supplies electric power to the first power source, and a second power supplying unit, which includes the main power switch and a second relay and supplies the electric power to the second power source. The electric power is supplied to the first power source by turning on the main power switch, and the first relay is turned on by a voltage output from the second power source. The electric power is supplied to the second power source by turning on the second relay by a voltage output from the first power source.