Inamoto was born in Osaka Prefecture on September 18, 1979. He joined J1 League club Gamba Osaka from their youth team in 1997. In April when at the age of 17, he debuted opening match in 1997 season, which made him the youngest player who played J1 League at that time. He played for Gamba until summer 2001 and played 118 matches in J1 League. In summer 2001, he moved to English Premier League club Arsenal FC. After that, he played many European club, Fulham, West Bromwich Albion, Cardiff City, Galatasaray, Eintracht Frankfurt and Stade Rennais. In 2010, he returned to Japan and joined Kawasaki Frontale. He played for the club in 5 season. In 2015, he moved to J2 League club Consadole Sapporo (later "Hokkaido Consadole Sapporo"). Although the club won the champions in 2016 and was promoted to J1, he could not play many matches from the 2016 season. In 2019, he moved to J3 League club SC Sagamihara. The club won the 2nd place in 2020 and was promoted to J2.