Gas measurement device

Breath diagnosis device includes a cell portion, a light source unit, a detection unit, and a control unit. The cell portion includes a first isotope of carbon dioxide, and a second isotope of carbon dioxide, a space in which the sample gas is introduced, including breath including. The light source unit to be incident light to the space. The light source unit, the wavelength of the light is varied in a wavelength range of less than 4.34 micrometers or 4.39 micrometers. The detector includes a first detection of the intensity of said passed through the space in which the sample gas is introduced light, a second detection of the intensity of said passed through the space in which the sample gas is not introduced light , to perform operations including. Wherein the control unit, the first detection result, on the basis of the second detection result, and calculates the amount of the ratio of the second isotope relative to the amount of the first isotope in the sample gas in .