An electric power supply system for a vehicle has an electric power line wired in a loop configuration. From the electric power line power is supplied to a load, and to another system which supplies control system power supply. One shutdown circuit is provided in a module connected to the loop configured power supply line. When the electric power line and the load are short circuited, the shutdown can isolate and shut down only the failure point. Further, when the car is not in use, by stopping the power supply to the load, current consumption can be restrained. In response to detection of a ground short and a failure of a connection of a connector, an over-current prevention of an electric power line, a simple construction can be provided and a low current consumption can be realized.