Recently, various products using bone conduction speakers have been developed. When such products are used, bone conduction speakers are placed on the cheekbone. This gives the advantage of hearing the bone conduction sound while using an ear protector in a noise environment. It also gives the advantage of hearing the sound of air conduction and bone conduction at the same time. Aural characteristics of the bone conduction speaker on the cheek bone were measured. Specifically, this study investigated the equivalent sound of the air conduction to the bone conduction sound. It was shown that the relation between the vibration of the bone conduction and the sound pressure of air conduction is linear. In addition, a listening test of Japanese words was conducted. It was shown that the subjects had clearly recognized them.