This donjon has three stories, three roofs, and a cellar, and was constructed in the latter period of such donjon’s in Japan. The techniques and materials are first-rate. The small donjon is the defense turret of the castle front and the side defense against rear attack and located in the place where NONOMARE (the lowers west side of the mountain) and SANNOMARE (inside of Horinouchi Park) areas can be observed. The small donjon is so named because the turret is the second important turret after the main donjon. Two fabulous dolphin-like fish are at the ends of the pinnacle of the roof and give the architecture of the castle its dignity.