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 connected to the main power supply path , a sub-terminal connected to the sub-power supply path , and one load terminal connected to the load unit , and the one load terminal is connected to one of the main terminal and the sub-terminal and the one load terminal is not connected to the other of the main terminal and the sub-terminal ; 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 connected to the main power supply path , a sub-terminal connected to the sub-power supply path , and one load terminal connected to the load unit , and the one load terminal is connected to one of the main terminal and the sub-terminal and the one load terminal is not connected to the other of the main terminal and the sub-terminal ; 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 . <EOS>