Abstract: A fuel supply device connects a fuel tank, which stores a fuel necessary for power of an engine, to a hand-operating pump inlet of the engine, connects an inlet opening of a filter can that includes the inlet opening and an outlet opening to a hand-operating pump outlet of the engine, connects the outlet opening to a slope terminal of a fuel-returning three-way pipe, connects a priority terminal of the fuel-returning three-way pipe to a fuel return port of the engine, and connects a discharge terminal of the fuel-returning three-way pipe to a high-pressure pump fuel inlet port of the engine, whereby heated fuel from the fuel return port of the engine is supplied, with priority, through the discharge terminal of the fuel-returning three-way pipe to the engine for combustion for saving energy and effectively improving operation performance of the engine.