A respiratory waveform analyzer (10), operable to analyze a respiratory waveform, which is generated based ON a temporal change of a concentration of a component in respiratory gas of a subject and includes: a respiratory gas concentration generator (100,210) which generates a concentration signal based ON an output signal from a sensor (50) that is placed to measure the concentration of the component a flatness calculator (220) which calculates a flatness indicative of flat degree of the respiratory waveform based ON a temporal change of the concentration signal and a reliability calculator (230) which calculates a reliability of the respiratory waveform based ON the flatness and the concentration signal.
