The oxalic acid aqueous solution filled in an electrolytic tank is electrolyzed with an electrolyzer to produce carbonic acid gas, while ultrasonic wave from an ultrasonic generator is applied to the produced carbonic acid gas bubbles, to form micro bubbles, which is dissolved in said oxalic acid aqueous solution, so as to easily produce carbonic acid gas solution with micro carbonic acid gas bubbles dissolved at a low cost said carbonic acid gas solution can substitute carbonated spring.