Continuous measurement of breathing impedance with extremely high precision is enabled by executing noise elimination. A loudspeaker 21 applies an air vibration pressure by an oscillation wave to an oral cavity, the oscillation wave being obtained by frequency-culling so executed that the oscillation wave has only the frequency component that is left after the culling is executed from a plurality of different frequencies and being generated by a pulse signal for pulse drive with pulses made positive and negative separately in correspondence to the time of exhalation and the time of inhalation. A pressure inside the oral cavity is detected and a breathing flow is detected, and a signal obtained by the detection is Fourier-transformed by a Fourier transforming means 32 to obtain a spectrum. A breathing high frequency component that contributes as a noise is obtained by an extracting means 33, using a spectrum that corresponds to a frequency component culled from the result of the Fourier transformation. This breathing high frequency component is subtracted from a spectrum that corresponds to a frequency component left by the culling to extract an oscillation wave component. Computing of dividing a pressure component by a flow component for each of frequencies for the result of this extraction is executed by a computing means 34 to obtain breathing impedance.
