Although still in his early twenties, Yoshioka was the first diplomat of the Ministry of Foreign Affairs after the So clan of the Tsushima Fuchu domain to be in charge of Japan's diplomatic relationship with Joseon and to negotiate with Joseon over the establishment of diplomatic relations between the two countries.
吉岡は20代前半の若さで対馬府中藩・宗氏から外務省に引き継がれた日朝外交の最初の担当者として国交樹立交渉に臨んだのである。