Jun Kokubo began playing as a midfielder during his senior career with the Montedio Yamagata, a club based in Japan and founded in 1984.
Montedio Yamagata (, Montedio Yamagata) is a professional association football club based in Yamagata Prefecture in Japan. 1984; 36 years ago (1984) He played many matches as midfielder from first season. After dropped out from Tokai University, he joined newly was promoted to J2 League club, Montedio Yamagata in August 1999. 
