Everything on the earth, from chemical compounds to living things, consist of about 100 kinds of chemical elements. Moreover, they are considered to have self-organized. In order to elucidate the mechanism of such self-organization we made a simple model. When self-organization occurs, there must be some information of the structures. We call the information "system description". Our model has 5 kinds of elements. If the elements are assembled to a system according to a system description, the system will have a specific function. When two system descriptions mate with each other accompanied by mutations. A new system appears. We devised the format of "system descriptions" and the mechanism of producing the structure corresponding to each system description. In our experiment several initial systems repeated mating and mutation during some generations to produce many kinds of systems each of which has its specific function. If natural selection is added to this model, it will be a model for evolution.<<ETX>>