An apparatus for exhaled gas measurement and analysis for measuring carbon dioxide 13 CO 2 concentration or concentration ratio of carbon dioxide 13 CO 2 to carbon dioxide 12 CO 2 through introducing a human exhalation including carbon dioxide 13 CO 2 and carbon dioxide 12 CO 2 as component gases into a cell and measuring intensities of light transmitted through the cell having wavelengths at which light is transmitted through the respective component gases, followed by data processing based thereon, the apparatus comprising: a gas inlet vessel for injecting into the cell the human exhalation collected in a breath bag that is capable of expanding and contracting; a first valve (V3, V4) for communicating the breath bag with the gas inlet vessel; a second valve for communicating the gas inlet vessel with the cell; valve driving means for driving the first valve (V3, V4) and the second valve; a pressure sensor for measuring a pressure inside the cell; gas inlet vessel driving means for sucking a predetermined volume of the exhalation into the gas inlet vessel; pressure measuring means for measuring a pressure of gas inside the cell by the pressure sensor, the cell being communicated with the gas inlet vessel through the second valve, when the first valve (V3, V4) is closed; measuring and analyzing means for performing exhaled gas measurement and analysis; wherein the apparatus is configured to perform the following: the pressure of the exhalation in the gas inlet vessel is measured by the pressure measuring means; if the pressure measured by the pressure measuring means is below an atmospheric pressure, then it is determined that the amount of the exhalation collected in the breath bag is insufficient and the measurement is cancelled; if the pressure measured by the pressure measuring means equals the atmospheric pressure, then the gas inlet vessel is pushed and the cell is filled with the exhalation. a gas inlet vessel for injecting into the cell the human exhalation collected in a breath bag that is capable of expanding and contracting; a first valve (V3, V4) for communicating the breath bag with the gas inlet vessel; a second valve for communicating the gas inlet vessel with the cell; valve driving means for driving the first valve (V3, V4) and the second valve; a pressure sensor for measuring a pressure inside the cell; gas inlet vessel driving means for sucking a predetermined volume of the exhalation into the gas inlet vessel; pressure measuring means for measuring a pressure of gas inside the cell by the pressure sensor, the cell being communicated with the gas inlet vessel through the second valve, when the first valve (V3, V4) is closed; measuring and analyzing means for performing exhaled gas measurement and analysis; wherein the apparatus is configured to perform the following: the pressure of the exhalation in the gas inlet vessel is measured by the pressure measuring means; if the pressure measured by the pressure measuring means is below an atmospheric pressure, then it is determined that the amount of the exhalation collected in the breath bag is insufficient and the measurement is cancelled; if the pressure measured by the pressure measuring means equals the atmospheric pressure, then the gas inlet vessel is pushed and the cell is filled with the exhalation. the pressure of the exhalation in the gas inlet vessel is measured by the pressure measuring means; if the pressure measured by the pressure measuring means is below an atmospheric pressure, then it is determined that the amount of the exhalation collected in the breath bag is insufficient and the measurement is cancelled; if the pressure measured by the pressure measuring means equals the atmospheric pressure, then the gas inlet vessel is pushed and the cell is filled with the exhalation.