For the study of evolutionary systems, we have already proposed several models. In this paper, we are concerned with a different type of evolutionary system, the cell-specialization. As seen in hydras, cell-specialization is one of the very important types of self-organization. In the process of cell-specialization, each cell which has the same DNA is specialized. The whole system which consists of these cells has a highly advanced function. We propose a kind of coding (something like DNA), ``a system description'' which makes this possible. Using the system description, we built a hardware model which shows the validity for self-organization, and also did some computer simulations which shows this can be used for evolutionary systems.