Sakontarō is a traditional device that uses flowing water to pound and polish rice. It is related to the karausu, a tool once used across Japan.

Its movement is similar to a shishi-odoshi, or deer scarer. As water fills a basin, a wooden pestle slowly lifts. When the water spills out, the pestle drops, repeating the motion and gradually polishing the rice.

While the exact installation date is unknown, it is said that rice polished here was eaten during the time of Shimazu Tadamoto, the 30th head of the Shimazu family.