A power supply device includes a main power supply, a sub-power supply, a main power supply path, a sub-power supply path, a power supply selector switch, and a load selector switch group. The main power supply path is connected to the main power supply. The sub-power supply path is different from the main power supply path and is connected to the sub-power supply. The load selector switch group is disposed between the main power supply path and the sub-power supply path, and the load unit, and performs switching so as to connect one of the main power supply path and the sub-power supply path to the load unit and to disconnect the other from the load unit, according to switching of the power supply selector switch.