Miyamoto first started his career playing for the team of Osaka Institute of Technology (currently: Joshou Gakuen High School) and then, for Doshisha University.
However, the achievements of the domestic teams, including the university period, ended in second place at the highest, and in his active period he was nicknamed The Battle General of Trouble (悲運の闘将, Hiun no Tōshō), especially in the Japan Company Rugby Football Championship final against Kobe Steel, where in the second half, the match finished in a draw after the Kobe Steel winger Ian Williams scored a try.
Lastly, during the 1994 Japan Company Rugby Football Championship final in January, Miyamoto retired from playing in the young age of 27 due to a knee injury.
In the 2005 season, Sanyo Wild Knights have won eight consecutive titles since the start, only to lose against Toshiba Brave Lupus in the Top League championship.
As from April 1, 2008, Miyamoto was appointed general manager of Sanyo Electric overseas sales division, being still focused on his company's business.