A method for producing ammonia includes dissolving air in water to obtain a two-phase coexistence aqueous solution with air that is pressurized and heated to a critical state to separate critical state nitrogen, critical state oxygen and critical water from the two-phase coexistence aqueous solution. The critical water is electrolyzed to obtain super critical state hydrogen and super critical state oxygen. The critical state nitrogen reacts with the super critical state hydrogen to produce ammonia. A device for producing ammonia includes a pressurizing member and a heating member mounted between a conversion unit and a mixing unit. The conversion unit outputs a critical state gas. A synthesis unit is connected to the conversion unit by a pipe allowing the critical state gas to flow into the synthesis unit. A gas outlet pipe is connected to the synthesis unit and outputs a synthesis gas from the synthetic unit.