In April 1967, he ran for the first time in an election for a member of the Saitama Prefectural Assembly from Kumagaya City.

[2] In May 1982, he resigned as a member of the Saitama Prefectural Assembly and ran for a mayor of Kumagaya City and was elected for the first time.

On the 6th of the following month, he ran as an independent from Saitama 3rd district in the 1986 Japanese general election for members of the House of Representatives, but failed.

[5] In the same year, Masuda was appointed Undersecretary of Land, Infrastructure and Transport under the Hosokawa Cabinet.

[7] On 6 January 2001, he became State Minister of Health, Labour and Welfare of the Second Mori Second Reshuffled Cabinet.