When Masakado called himself the 'new emperor' and caused a insurrection in January, on February 29, 940 Kinmasa became one of the eight Kokushi (provincial governor) of Togoku (the eastern part of Japan) who were assigned to divert Masakado, and after the Taira no Masakado Rebellion was suppressed, he became the Kokushi of Awa Province.
12月に将門が「新皇」を自称し叛乱をおこすと、翌天慶3年（940年）1月14日、将門の牽制の為に任命された8人（坂東8ヶ国）の東国国司の一人となり、将門の乱の鎮圧後に安房国国司となった。