The main buildings of the important Buddhist temples - the pagoda, the Buddhist sanctum, the lecture hall - was surrounded by the cloister until Koryo Dynasty. And the Buddhist sanctum was located the center. It meant that the Buddhist sanctum was important building. It is very important thing that we understand the usage of the interior space because the architectural space consists of the unified space by the organic function of the interior space and the exterior space. But there is not so much the study on the interior space of the Buddhist sanctum. So, the purpose of this study is to understand of the interior space of the Buddhist sanctum in Ancient and Medieval Times. Till now, it was impossible that the Buddhist monk or the General public entered the Buddhist sanctum in Ancient and Medieval Times because they regarded the Buddhist sanctum as the place of sacrosanctity and the floor was finished by bricks. But, we saw that they could enter the Buddhist sanctum. Of course the floor of the Buddhist sanctum was finished by bricks, but they spread mats on the floor, took off his shoes in the interior space and used the furniture for sitting on. The plan of the Buddhist sanctum was designed by the process of the ceremony and the way of the enshrinement of the Buddhist statues because it is the place to enshrine the Buddhist statues. They performed the ceremony like as pray, worship, offer food to Buddha, HaengDo - an act to turn round an object of worship - and so on in the interior space of the Buddhist sanctum.