A fuel supply device, which supplies fuel necessary for an operation of a rotary high-pressure fuel distribution engine, comprising: a return fuel utilization buffer jar, which comprises a hollow jar portion and a buoy arranged in interior of the hollow jar portion, the hollow jar portion having a lower portion in which a return fuel inlet port and a return fuel outlet port in communication with the interior are formed, the hollow jar portion having an upper portion in which a fuel vapor recovery hole in communication with the interior is formed, wherein the return fuel inlet port functions to conduct in return fuel from the rotary high-pressure fuel distribution engine and vapor of the return fuel vapor is conducted out, through the fuel vapor recovery hole and wherein when a liquid level of the return fuel in the hollow jar portion is higher than a threshold level, the buoy is moved by buoyance to open a passage so as to allow the return fuel in the hollow jar portion to flow through the return fuel outlet port; characterized in that a first three-way valve comprises a fuel inlet port, a fuel outlet port, and a return fuel receiving port, a reversal flow prevention device being arranged between the fuel inlet port and the fuel outlet port that constrains fuel to flow, in one direction, from the fuel inlet port to the fuel outlet port, the fuel outlet port and the return fuel receiving port being connected to and in communication with each other, wherein the return fuel in the hollow jar portion flowing through the return fuel outlet port is conducted through the return fuel receiving port of the first three-way valve to the rotary high-pressure fuel distribution engine; and a second three-way valve comprises a gas inlet port, a gas outlet port, and a ventilation port, a one-way reversal flow prevention device being arranged between the ventilation port and the gas inlet port. a return fuel utilization buffer jar, which comprises a hollow jar portion and a buoy arranged in interior of the hollow jar portion, the hollow jar portion having a lower portion in which a return fuel inlet port and a return fuel outlet port in communication with the interior are formed, the hollow jar portion having an upper portion in which a fuel vapor recovery hole in communication with the interior is formed, wherein the return fuel inlet port functions to conduct in return fuel from the rotary high-pressure fuel distribution engine and vapor of the return fuel vapor is conducted out, through the fuel vapor recovery hole and wherein when a liquid level of the return fuel in the hollow jar portion is higher than a threshold level, the buoy is moved by buoyance to open a passage so as to allow the return fuel in the hollow jar portion to flow through the return fuel outlet port; characterized in that a first three-way valve comprises a fuel inlet port, a fuel outlet port, and a return fuel receiving port, a reversal flow prevention device being arranged between the fuel inlet port and the fuel outlet port that constrains fuel to flow, in one direction, from the fuel inlet port to the fuel outlet port, the fuel outlet port and the return fuel receiving port being connected to and in communication with each other, wherein the return fuel in the hollow jar portion flowing through the return fuel outlet port is conducted through the return fuel receiving port of the first three-way valve to the rotary high-pressure fuel distribution engine; and a second three-way valve comprises a gas inlet port, a gas outlet port, and a ventilation port, a one-way reversal flow prevention device being arranged between the ventilation port and the gas inlet port.