PROBLEM TO BE SOLVED: To provide an expired gas analyser that obtains expired gas analysis data by measuring a flow rate of respiratory air and gas concentration of a subject by solving a problem of an error detected in expired gas analysis data due to variation of a time lag td caused by various factors even though the time lag td needs to e obtained accurately to compensate for delayed measurement of gas concentration in relation to a flow rate.SOLUTION: An error factor such as fluctuation is eliminated by discharging a calibration gas in a pulse state at fixed intervals many times and averaging time lags.
