On November 7, 720, when the murder of KAMITSUKENO Hiroto, Inspector of Mutsu (Mutsu no Azechi) occurred in Mutsu Province, Iwashiro who had been sakyo no suke (a governor who supervised central administration, security and administration of justice) and ranked as Jugoinoge (Junior Fifth Rank, Lower Grade) was appointed to Seii fukushogun (sub commander of the expeditionary force against the barbarians) by the Empress Gensho and conquered it.
720年（養老4年）9月29日(旧暦)-陸奥国で起きた陸奥按察使上毛野廣人殺害事件に対し、この時左京亮従五位下であった石代は元正天皇より征夷副将軍に任ぜられ、これを征伐する。