To efficiently remove carbon dioxide stably at a lower cost and make effective use of the removed carbon dioxide.

The system for gas treatment is provided with a gas treatment apparatus 1, a regenerating tank 5 and a route for supplying a sodium hydroxide aqueous solution produced in a cathode chamber of the tank 5 to the apparatus 1. The apparatus 1 is provided with an electrolytic membrane 10 through which sodium ions are permeated, an anode 11 to which an aqueous solution of a sodium compound is supplied and a cathode 12 to which the gas to be treated is supplied and is used for separating/removing the carbon dioxide in the gas to be treated as the form of a carbonate on the side of the cathode 12 by applying DC voltage between the anode 11 and the cathode 12. The tank 5 is provided with another electrolytic membrane through which the sodium ions are permeated, an anode chamber and the cathode chamber which are formed by arranging the electrolytic membrane, a route for supplying the aqueous solution of the carbonate separated/removed in the apparatus 1 to the anode chamber and a route for supplying water to the cathode chamber and is used for producing sodium hydroxide in the cathode chamber by applying DC voltage between the liquid in the anode chamber and that in the cathode chamber.