A respiratory waveform analyzer, 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, includes: a respiratory gas concentration generator which generates a concentration signal based on an output signal from a sensor that is placed to measure the concentration of the component a flatness calculator 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 which calculates a reliability of the respiratory waveform based on the flatness and the concentration signal.
