The purpose of this paper is to clarify the formation and the development process of the function of the Ogakumon-jo in the imperial palace. In this study, I tried to indicate the formation in the period of emperor Gohanazono and the importance as a private space for the reading rites. A summary will be given as follows : 1. The Ogakumon-jo as a private space for the reading rites was formed at the Oeido-Dairi in the period of emperor Gohanazono. 2. After the Onin Civil War, the Ogakumon-jo was used as a space for the various studies and exercises. 3. The Ogakumon-jo came into use as one of the space for the private reception from the second half of the 15th century. 4. A size of the room where was used for the Ogakumon-jo was unchangeable from the period of emperor Gohanazono till the period of emperor Gokasiwabara.