Through an electrical resistance tomography method, it was possible to determine the phase inversion phenomenon, from water-in-oil (50 vol%) to oil-in-water, by dynamically varying the impeller rotational speed in a stirred vessel attached with a 6-blade paddle impeller. Accordingly, it was found that the water-in-oil and oil-in-water states replace each other continuously and reversibly up to a certain point, and then the replacement become irreversible thereafter.