After passing the Taisaku (an examination for adopting government officials under the Ritsuryo legal codes), Arimasa consecutively worked in different positions, including Naiki (Secretary of the Ministry of Central Affairs) and Monjo hakase (professor of literature), later reaching the rank of Jushiinojo (Junior Fourth Rank, Upper Grade) with a post in the Shikibu-sho (the Ministry of Ceremonial).
対策を経て、内記・文章博士などを歴任し、その後、従四位上式部省に至った。