Abstract: Provided is a white-cell type non-dispersive infrared gas sensor and more particularly, a non-dispersive infrared carbon dioxide gas sensor deposited with a hydrophobic thin film. To this end, in a carbon dioxide gas sensor for measuring a concentration of carbon dioxide included in gas, the gas sensor is a white-cell type, in the white-cell, first and second reflectors 120 and 130 are disposed to face a third reflector 140, a light source 110 is provided at one side of the third reflector 140 and a first detector 150 and a second detector 160 are provided at the other side. Further, a first hydrophobic thin film 122 may be deposited on the entire reflection surface of the first reflector 120, a second hydrophobic thin film 132 may be deposited on the entire reflection surface of the second reflector 130, and a third hydrophobic thin film 142 may be deposited on the entire reflection surface of the third reflector 140.