Matsui Keishirō (Japanese: 松井慶四郎, 28 March 1868 - 4 June 1946) was a Japanese diplomat during the Showa period and later Minister of Foreign Affairs. He graduated from the Law School of Tokyo Imperial University in 1889, and entered the Foreign Ministry the same year. In 1890, he was given a post in the Japanese embassy in Seoul in 1890, and in 1895 was sent to the United States. In April 1889, he served in London. In 1902, he was re-assigned to Beijing. He returned to Japan in 1913.
During World War I, Matsui served as Japanese Ambassador to France from November, 1915. When he finished this mission, he was awarded with the title of baron (danshaku) under the kazoku peerage system. He served as Minister of Foreign Affairs from 7 January to 11 June 1924 under the government of Kiyoura Keigo.
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