Born in Hyogo Prefecture,[2] Ienaga began his career as a trainee with Gamba Osaka, one of the leading clubs in Japan's J1 League. He broke into the senior squad in 2004 and helped the club to their first J1 League title the following year. Ienaga joined J1 League rivals Oita Trinita on a season-long loan in 2007. In December 2008, Ienaga joined English club, Plymouth Argyle, on trial.[3] Plymouth attempted to sign the player in January 2009 but he was denied a work permit so they were forced to withdraw from talks.[4] In December 2010, he signed with Spanish Primera Division club RCD Mallorca in a five-year deal.[5] And scored his first goal for the club in home game against Sevilla on 9 April 2011.[6]