Shinjirō Koizumi (Japanese: 小泉 進次郎, Hepburn: Koizumi Shinjirō; born 14 April 1981) is a Japanese politician serving as the Minister of Defense since October 2025. He previously served as the Minister of the Environment from September 2019 to October 2021 and Minister of Agriculture, Forestry and Fisheries from May to October 2025. He has also served as a Member of the House of Representatives for the Liberal Democratic Party, representing Kanagawa since 2009. He is the second son of former Prime Minister Junichiro Koizumi and the younger brother of actor Kotaro Koizumi.
After graduating from university, Koizumi worked as a researcher at the Washington-based think tank Center for Strategic and International Studies, and became active politically as Young Leader of the Pacific Forum CSIS. He also spent time working as a political secretary for his father in the final years of his second term as prime minister. In the 2009 election, he was elected to the House of Representatives for the seat his father had occupied for more than 35 years.
