Kajiyama was born in Koto, Tokyo on September 24, 1985. He joined FC Tokyo from their youth team in 2003. He debuted in 2003 and played many matches from 2004. FC Tokyo won the champions in the 2004 J.League Cup first major title in the club history. He became a regular defensive midfielder in 2005 and played many matches every season. He was given "number 10" shirt in 2008. FC Tokyo won the champions in the 2009 J.League Cup. However FC Tokyo finished at 16th place in the 2010 season and was relegated to J2 League. In 2011, FC Tokyo won the champions and was returned to J1 in a year. FC Tokyo also won the champions in 2011 Emperor's Cup.