The object of this research is to clarify the trade relationship between Britain and Japanese feudal lords at the end of the Edo period in the middle of the 19th century. In 1858, the Japanese feudal government, Tokugawa shogunate, having a national isolation policy, made a commercial treaty with foreign countries and started trading with them. As the government had a monopoly on the trade at some specified open ports, foreign countries insisted that some ports in territories of feudal lords, specifically the Shimonoseki Port of the Choshu Clan, were opened. After the government refused, it was directly negotiated between Britain and the Choshu Clan. From the viewpoint of the Choshu Clan, it is difficult to say that the Choshu Clan offered it to Britain in a positive way as if they had the desire. However, from the viewpoint of Britain, it became clear that the Choshu Clan offered Britain the use of Shimonoseki Port in order to trade directly with foreign countries. Because of the different results, it is considered Britain needed to take measures to emphasise that the Choshu Clan desired to open the Shimonoseki Port, in order to make the Tokugawa government allow feudal lords to trade with foreign countries directly, regardless of the actual motivation on the part of the Choshu Clan.