According to Article April 12 of 1199 which MINAMOTO no Yoriie who succeeded Yoritomo decided to stop the direct involvement in lawsuits, and 13 senior vassals became in charge of settling a matter through discussion, Minbu no Taifu Yukinari was listed among the vassals along with OE no Hiromoto and MIYOSHI no Yasunobu, indicating that Yukimasa was one of the governmental bureaucrats responsible for practical work to support the early stage of the Kamakura Government.
1199年（正治元年）4月12日条には頼朝の跡を継いだ源頼家が直に諸訴論に関与することを停止し、13人の重臣が合議して決定することになったとあるが、その中に民部大夫行政の名も入っており、大江広元、三善康信と並んで初期鎌倉政権を支えた実務官僚であったことが解る。