To provide a method for producing a high-quality water-oil mixed liquid fuel obtained by mixing the high-quality water with a fossil fuel such as a petroleum, a dust coal, a fish oil, a vegetable oil and a liquid fuel oil such as an alcohol.

The water-oil mixed liquid fuel produced from the water and the fossil fuel, or the like, is produced by integrally mixing the water with the oil at first by adding an additive and the fossil fuel to the water in a vessel for mixing and stirring the water, the oil, and the like, by generating ultrasonic waves in the water while heating, transferring the resultant mixture to a reaction vessel 1 having several containers 9 attached to the bottom surface of the reaction vessel, including a Brown's gas pressurized and sealed therein, and having 11-21 volumes to improve the quality and properties of the mixed liquid fuel, charging the reaction vessel 1 with the mixed liquid fuel, completely sealing the reaction vessel 1 charged with the liquid fuel, injecting the pressurized Brown's gas from a Brown's gas-injecting opening 3 after the complete sealing is confirmed, completely sealing the opening 3, and igniting the Brown's gas by an igniting device 4 to momentarily burn out the Brown's gas by forming super fire and detonation pressure to form vacuum. The water-oil mixed liquid fuel is produced by utilizing the power.