A purpose of this paper is to clarify the architectural characteristics of Io-ji Temple, the Matsui family’s place of prayer, in Yatsushiro City. The temple keeps many cultural properties, and the Main hall itself is a cultural properties designated by Yatsushiro City. But there was not an investigation about the architecture until now. We made the survey drawings, arranged the historic change and compared that with the other prayer’s places in Yatsushiro City. The Main hall was built in 1665. It is the biggest and the most prestigious architecture for the place of prayer in Yatsushiro City. Particularly, the gate for the Matsui family exists.