A power supply device comprising: a main power supply that supplies power to a load unit; a sub-power supply that is a power supply different from the main power supply and supplies power to the load unit; a main power supply path that is connected to the main power supply; a sub-power supply path that is a power supply path different from the main power supply path and is connected to the sub-power supply; a load supply path selector that 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 disconnect the other of the main power supply path and the sub-power supply path from the load unit, wherein the load supply path selector includes a main terminal (71a, 72a) connected to the main power supply path, a sub-terminal (71b, 72b) connected to the sub-power supply path, and one load terminal (71c, 72c) connected to the load unit, and the one load terminal (71c, 72c) is connected to one of the main terminal (71a, 72a) and the sub-terminal (71b, 72b) and the one load terminal (71c, 72c) is not connected to the other of the main terminal (71a, 72a) and the sub-terminal (71b, 72b); characterized by: a power supply selector switch that is disposed between the load path selector on a side of the sub-power supply and the sub-power supply, wherein when the power supply selector switch is turned on, power is supplied from the main power supply via the main power supply path, and when the power supply selector switch is turned off, power is supplied from the sub-power supply via the sub-power supply path to the load unit, and the load supply path selector performs switching according to switching of the power supply selector switch. a main power supply that supplies power to a load unit; a sub-power supply that is a power supply different from the main power supply and supplies power to the load unit; a main power supply path that is connected to the main power supply; a sub-power supply path that is a power supply path different from the main power supply path and is connected to the sub-power supply; a load supply path selector that 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 disconnect the other of the main power supply path and the sub-power supply path from the load unit, wherein the load supply path selector includes a main terminal (71a, 72a) connected to the main power supply path, a sub-terminal (71b, 72b) connected to the sub-power supply path, and one load terminal (71c, 72c) connected to the load unit, and the one load terminal (71c, 72c) is connected to one of the main terminal (71a, 72a) and the sub-terminal (71b, 72b) and the one load terminal (71c, 72c) is not connected to the other of the main terminal (71a, 72a) and the sub-terminal (71b, 72b); characterized by: a power supply selector switch that is disposed between the load path selector on a side of the sub-power supply and the sub-power supply, wherein when the power supply selector switch is turned on, power is supplied from the main power supply via the main power supply path, and when the power supply selector switch is turned off, power is supplied from the sub-power supply via the sub-power supply path to the load unit, and the load supply path selector performs switching according to switching of the power supply selector switch. a power supply selector switch that is disposed between the load path selector on a side of the sub-power supply and the sub-power supply, wherein when the power supply selector switch is turned on, power is supplied from the main power supply via the main power supply path, and when the power supply selector switch is turned off, power is supplied from the sub-power supply via the sub-power supply path to the load unit, and the load supply path selector performs switching according to switching of the power supply selector switch.