Provided is a gas sensor comprising first and second light emitting parts, first and second light receiving parts, a first optical path region and a second optical path region, wherein the optical path regions have a common region, an optical path length of the first optical path region is longer than that of the second optical path region, a rate of change of an output signal with respect to a gas to be measured of the first light receiving part is larger than that of the second light receiving part, a rate of change of an output signal with respect to an interference gas of the second light receiving part is larger than that of the first light receiving part, and a sensitivity peak wavelength of the second light receiving part overlaps with an absorption wavelength of water vapor.