In this paper, a measurement of the difference between air-conduction and bone-conduction transfer functions was performed. The transfer function was measured by canceling air-conduction and bone-conduction sound each other. The transfer function was measured for 30 kinds of frequencies ranging from 100 Hz to 15 kHz for 6 subjects. From the results, the frequency characteristics of amplitude difference measured using all subjects have the common dip at approximately 3 kHz and peaks at 3 to 7.5 kHz in this case, and the cepstrum insists that the BC sound arrives to the inner ear 0.2 ms prior to the AC sound. The frequency characteristics of phase differences have the linear part, and it would indicate that AC and BC sound would have different propagation time. With these differential transfer functions, the spatial audio can be realized by compensating BC sound as if it is AC sound.