To contribute to environmental protection by producing an emulsion fuel oil by mixing distilled spirit lees, which are industrial wastes, inhibited ocean disposal from January 1, 2007 with plant-derived edible oil, petroleum-derived waste oil or new oil and by effectively using the distilled spirit lees.

The emulsion fuel oil Fb is obtained by agitating and mixing the plant-derived edible oil B, which is stock oil, petroleum-derived waste oil or new oil B' with distilled spirit lees liquid (a) in a mixing tank 2 each at a ratio of substantially 1:1 in the volume ratio, producing emulsion liquid F by radiating this with ultrasonic wave from an ultrasonic transmitter 20 so as to emulsify it, and circulating and passing the emulsion liquid F through a micro-bubble generator 30 so as to make a nano-size bubbling state.