Teaching Japanese students to sing the Western songs requires special consideration of difference between the Japanese language, which is pitch-oriented, and the Western languages such as Italian, German, French, Russian and English, which are accent-oriented. Singing can be seen as a process of converting one's breath into voice. In emitting the breath, a Western language speaker has to make full use of his/her diaphragm, which serves as an air pump, while a Japanese speaker does not necessarily have to. Without skills of using diaphragm, which a Western language speaker would naturally acquire, a Japanese student tends to have a voice with little or no resonance and, consequently, his/her ability to hear the resonance remains undeveloped. In this study, an attempt has been made to teach these skills by having the students play the keyboard harmonicas. In such training, it is difficult to make the students understand the concept by their own voices since there are too many variables in individual techniques and physical factors such as their bone structures, vocal cords or muscles. On the other hand, the keyboard harmonica is a simple instrument which students can easily play by blowing their breath into it, yet the sound each student produces has distinctly different resonance from one another. Using the instrument as a common item makes it easier to focus on the co-relation between the diaphragm movement and the difference in resonance. In the first solfeggio lesson of the first semester, each student's voice was recorded in order to evaluate his/her ability to recognize the resonance related to the use of diaphragm. After twelve lessons using keyboard harmonicas, the voice was recorded again for analysis of any changes in the student's ability.