Since the latter half of 1980s, many universities have set up the centers for lifelong learning. Those centers have worked as the special agencies for university extension. This paper aims to inquire how university extension has been accepted, and how it is institutionalized as the third function of the university through examining administrative system of those centers. Findings are as follows. (1) The administrative forms of university extension centes are classified into six types. (2) There is a great difference between national universities and private universities on administrative forms of centers. (3) Generally, the centers for lifelong learning are not placed in the core, but on the margines of the universities. (4) In the light of autonomy, the centers for lifelong learning are ranked lower than colleges on the same campus. (5) Considering from remarks of A. Levine and J. Carey, present condition of university extension is at early stage of its historical development.