Abstract: A carbonated spring producing coupler 100 comprising: a housing 10; a fluid guide path 20 that is formed by an inner wall of the housing 10 and extends in the housing 10; a hot water inlet opening 21 which is provided at one end of the housing 10 to allow the hot water to flow in; a carbon dioxide supply hole 50 for supplying carbon dioxide; a carbonated spring outlet opening 22 which is provided at another end of the housing 10 to discharge the carbonated spring produced by mixing the hot water and the carbon dioxide; a vane member 30 which is provided in the fluid guide path 20. The inner wall of the housing 10 has an inward protrusion 15 that protrudes inwardly. The carbon dioxide supply hole 50 is provided downstream of a farthest protruding vertex of the inward protrusion 15 in a direction in which the hot water flows.