Abstract: [PROBLEMS] To provide a fuel consumption reduction system capable of stable enhancement of mileage and a method of fuel consumption reduction. [MEANS FOR SOLVING PROBLEMS] Water and an adulterant are put in an ionic active water tank to thereby obtain ionic active water, and steam from the ionic active water is fed to the vicinity of an inlet of an internal combustion engine. At that stage, heat from a radiator, muffler, etc. is applied to a steam generator for generation of the steam so as to, while accelerating the steam generation, regulate the rate of steam generated. Thus, steam can be fed in an appropriate rate to the internal combustion engine.