Ienaga was born in Hyogo Prefecture on June 13, 1986. He joined J1 League club Gamba Osaka from their youth team in 2004. He played many matches as left side midfielder. The club won the champions in the 2005 J1 League and 2007 J.League Cup. In 2008, he moved to Oita Trinita. Although he could not play many matches for injury in 2008, he played many matches in 2009. However the club was relegated to J2 League end of the 2009 season. In 2010, he moved to Cerezo Osaka and played many matches. In January 2011, he moved to Spanish La Liga club Mallorca. Although he played many matches in the 2010/11 season, he could not play many matches in the 2011/12 season. In February 2012, he moved to South Korean K-League club Ulsan Hyundai on loan. In summer 2012, he moved to his first club Gamba Osaka on loan. However the club was relegated to J2 end of 2012 season. In summer 2013, he returned to Mallorca in Segunda División. In January 2014, he returned to Japan and joined Omiya Ardija. Although Omiya was relegated to J2 end of 2014 season, returned to J1 in a year. In 2017, he moved to Kawasaki Frontale. In 2017, Kawasaki won the J1 League first time in the club history. In 2018, Kawasaki won the champions for 2 years in a row and he was selected MVP award.