Ienaga began his career at Gamba Osaka, where he belonged to the senior squad in 2004. For the seasons 2008 and 2009, he was loaned to the J. League rivals Oita Trinita. After the descent from Oita Trinita from the Premier League, he was awarded for the 2010 season to the upstart Cerezo Osaka. In January 2011, he left Gamba Osaka and finally moved to RCD Mallorca. There, however, Ienaga was difficult to gain a foothold and spent the year 2012 completely in his homeland, each loan at Ulsan Hyundai FC and his former employer Gamba Osaka.
Ienaga debuted on March 24, 2007, in the match against Peru in the Japanese national soccer team.