Abstract: Disclosed is a fuel supply device for a diesel engine comprising alternately connected to a diesel engine a light fuel loop and a heavy fuel loop incorporating a tank and a fuel priming pump, the loops communicating with a suction pipe of the diesel engine via a system of stop valves. The light fuel loop is in communication with the diesel engine. The system of stop valves comprises a logical element "OR", the output thereof being connected to the suction pipe of the diesel engine, a pressure controller connected to the first input of the logical element "OR", a flow switch valve having its input connected to the second input of the logical element "OR" and to the fuel priming pump of the heavy fuel loop. The output of the flow switch valve communicates with the tank of the heavy fuel loop.