Synchronization between movement and voice is indispensable for both communication among people and improvement of the efficiency of joint working The first object of this research is to develop a quantitative and objective analysis method for movement-voice synchronization by introducing an image analysis method using computers. As an example, mother-neonate (new-born baby) communication, which is one of the primitive forms of communication, is selected as an object to be studied. Secondly, a model of the mother-neonate communication is proposed. The model depends upon the control theory, and its fundamental mechanism is discussed. It is considered that this study will give us a key to the quantitative solution about the synchronization of joint working by voice.