 He represented Osaka Prefecture in the 26th in March 2001 and then entered the Japan Shogi Association's apprentice school in September of that same year at the rank of 6-kyū as a student of shogi professional .He was promoted to the rank of 1-dan in July 2001.Ōishi was promoted to 3-dan in 2006 and finished the 40th 3-dan League (October 2006March 2009) tied for third place with a record of 13 wins and 5 losses.