Myojin was born in Kobe on January 24, 1978. He joined J1 League club Kashiwa Reysol from their youth team in 1996. He played many matches as defensive midfielder from first season. He became a regular player under manager Akira Nishino in 1998. In 1999, Reysol won the champions in J.League Cup and the 3rd place in J1 League. In 2000, Reysol won the 3rd place in J1 League for 2 years in a row and he was selected Best Eleven award. However the club results were sluggish from 2002 and was relegated to J2 League end of 2005 season.
In 2006, Myojin moved to Gamba Osaka which was managed by Akira Nishino. He played as regular player with many Japan national team player and Gamba won the many title, 2007 J.League Cup, 2008 and 2009 Emperor's Cup. In Asia, Gamba also won the champions in 2008 AFC Champions League and the 3rd place in 2008 Club World Cup. This is the golden era in the club history and he was one of the central player under manager Nishino. However manager Nishino left Gamba end of 2011 season and the club performance deteriorated soon. In 2012, Gamba finished at the 17th place of 18 clubs and was relegated to J2 League. Although his opportunity to play decreased from 2013, Gamba won the champions in 2013 J2 League and was returned to J1. In 2014, Gamba won all three major title in Japan, J1 League, J.League Cup and Emperor's Cup. He resigned end of 2015 season.
In 2016, Myojin moved to Nagoya Grampus. However he could not play many matches. Grampus also finished at the 16th place and was relegated to J2. In 2017, Myojin moved to J3 League club AC Nagano Parceiro; after three seasons, he retired at the end of 2019.
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