The purpose of this article is to investigate the function of "School Knowledge" as Socialization from viewpoint of theory on "Hidden Curriculum." and then, I will show the limitation of that theory. The agenda of educational reform in Japan intends to realize some privatization or to introduce the principle of a market mechanism in the system of compulsory education. But rethinking about the function of Socialization in public schools is most important to solve so-called educational problems in these days. The morality, which is to study in the same time and spacewith same materials, will be investigated, and then, I will show that the structural defect in schools is the key concept to maintain the publi education.