According to evaluation of tone quality of exhaust sound adapted to human audition, a characteristic of the tone quality of exhaust sound is objectively analyzed. There are provided a measuring process (M1) for sampling exhaust sound to be analyzed, by means of a microphone disposed in an exhaust system EX and converting the exhaust sound into an electric signal, an analyzing process (M2) for amplifying a high frequency component of the electric signal and performing a frequency analysis of the electric signal at an arbitrary time interval, a detecting process (M3) for detecting a first formant of the first peak from the low frequency side and a second formant of the second peak from the low frequency side, and a displaying process (M4) for displaying a relationship (brightness and sharpness) between the first formant and second formant in a predetermined time range.