This is the only Unjo House that exists in Hokkaido. The building was established as a base for the management of Ezo by the Japanese as well as a facility for trade and petting with the Ainu. It is a nationally designated cultural property.

The Unjo-ya was the base of operations for merchants contracted by the Matsumae clan to trade with the Ainu people during the Edo period, and was built at various locations in Ezochi. The old Shimo-Yoichi Unjyoke was built in 1853 by Takeya Hayashi Chozaemon, a contract merchant in the Yoichi area, and is the only surviving Unjyoke in the area. The long gabled, flat-roofed stone roof, lattice windows, and paper sliding doors are of the same design as those of Hokuriku fishing house architecture.

The interior space is spacious, and the pillars and beams looking up from between the boards are thick, many of whose members are still in use from the period. The building has a frontage of 40 meters, a depth of 16 meters, a building area of 534 square meters, and 213 cubic meters of lumber used. In the tatami rooms located on both sides of the corridor, dolls depicting the manners and customs of the managers dispatched by the contractor and the samurai of the Matsumae domain are on display.