The Marumou Family Lower Mansion is the symbol of Usuki, a former castle town. It was once the mansion of a high-ranking samurai who had defined its late-Edo period architectural style.

The Marumou family were samurai of the former Mino clan (in today's Gifu Prefecture), and were once in service to Mitsuhide Akechi. After Mitsuhide was defeated by Hideyoshi Toyotomi during the Battle of Yamazaki in the 10th year of the Tenshou era (1582), the family was homeless for many years.

The family made a comeback in the 5th year of the Kannei era (1628) during the Edo period. Because the first leader of the Usuki clan, Sadamichi Inaba, was related to the Marumou family, they were taken in by them. Soon after, the Marumou family came to reign as one of the highest-ranking samurai families in the Usuki clan.

One of the main characteristics of the Marumou Family Lower Mansion is that the house is completely divided by walls into several parts, including an 'omote' for guests, and an 'oku' for living quarters. Not only individual rooms but the entrance also is divided, for guests and family. One can see how seriously the samurai family took tradition and ceremonies.