PREFERENCE CIRCUIT AND ELECTRIC POWER SUPPLY SYSTEM

There is provided a prioritization circuit 60 which selects one of a system power supply 100 and a secondary battery unit 30 as a selected supply source and the other as a non-selected supply source and which causes supply of electric power with a higher priority from the selected supply source to a power supply unit 52, wherein the non-selected supply source is connected to the power supply unit 52 through a diode element 74 which generates a voltage drop and the selected supply source supplies electric power to the power supply unit 52 without passing through a diode element 84.