A device is discussed in which tubal opening as one of the functions of the Eustachian tube can be measured by expressing the opening phenomena acoustically. The features of the present device are the following: introduction of the test sound of 2,000 Hz, 85 dB, SPL, directly to the tubal opening through the tubal catheter and recording of fluctuations of the sound pressure obtained at the external auditory meatus during swallowing. The results of model experiment made of resin were 85 dB, SPL, at the speaker, 76 dB, SPL, at the end of tubal catheter and 78 dB, SPL, at the external auditory meatus. In the model experiment it was also demonstrated that the height of spike waves depends on the extent of tubal opening and that the continuity of spike waves depends on the duration of tubal opening. Furthermore, in the present method, there was no so-called basic amplitude, seemingly due to the resonant effects or the direct passing sound, and the opening phenomena were correctly expressed. In the measurement on normal adults it was found that variability of the spike wave pattern between subjects was largely depending on individual subjects, and also some intra-subject variability of successively recorded spike waves on the same subject was noted. It was shown that gradual recovery of spike wave patterns occurred from initial water swallowing to successive dry swallowing.