In 1856, when Masayoshi HOTTA became the head of Roju (senior councilor of the Tokugawa shognate) and came to be in charge of foreign affairs, Nishimura was appointed to Boeki Torishirabe Goyogakari (general affairs official of the Imperial Household in charge of trade) to handle classified diplomatic documents.
1856年（安政3）、堀田正睦が老中首座・外国事務取扱となると、貿易取調御用掛に任じられ、外交上の機密文書を担当。