disclosed is a portable spirometer which comprises : a small breath tube for measuring a unidirectional flow , to which the breath flow of a patient is inputted ; a breath signal processing unit which generates a breath signal from the breath flow , removes the noise contained in the breath signal and amplifies the signal level so as to generate a target signal of analysis ; a breath signal analysis unit for analyzing the target signal of analysis to calculate diagnosis parameters ; and a display unit for displaying the analysis result of the breath signal .