A fire engine or a truck carrying a fire extinguishing system having a device for supplying a powder fire extinguishing agent coated with a waterproof film, e.g., a silicone resin, and a fire-fighting water delivery pipeline, is used. The powder fire extinguishing agent is added and mixed into the fire-fighting water delivery pipeline, and mixed water is delivered through a fire house and discharged from a spray nozzle provided at the distal end of the fire hose.