Nishio was born in Ōno, Hokkaidō, now part of the city of Hokuto. After graduating Kyoto University, he became a public servant in 1973. He was appointed deputy mayor of Hakodate by its then-mayor Hiroshi Inoue in July 2003, but resigned himself in December 2006 due to a rift with the mayor over the construction of a retirement home. He beat Inoue in the mayoral election held on 22 April 2007, and took office on 27 April.
- 函館戦争. Zaikai Sapporo (in Japanese). 46: 198–203. May 2008.
- "西尾正範-ザ・選挙/立候補予定者情報-". ザ･選挙 (in Japanese). JANJAN. Retrieved 11 June 2009.
- "庁内対決"となった函館. Tokachi Mainichi Newspaper (in Japanese). Obihiro, Hokkaido: Tokachi Mainichi Newspaper. 19 April 2007. Retrieved 11 June 2009.
| Mayor of Hakodate
27 April 2007–present
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