A liquid medicine of the present invention comprising liquid having carbon dioxide dissolved therein, the liquid being administered by using means of liquid injection, and a method of treatment of the present invention using a liquid medicine comprising liquid having carbon dioxide dissolved therein, the liquid being administered by using means of liquid injection can reduce or eliminate tumors with few side effects. When the liquid medicine of the present invention comprising liquid having carbon dioxide dissolved therein, the liquid being administered by using means of liquid injection, and the method of treatment of the present invention using a liquid medicine comprising liquid having carbon dioxide dissolved therein, the liquid being administered by using means of liquid injection are used in combination with surgical therapy, chemotherapy, radiotherapy, or immunotherapy of tumors, effects can be enhanced or side effects can be reduced compared with monotherapy or multidisciplinary therapy thereof.
