After graduating from Hosei University, he joined Nissan Motors (later Yokohama Marinos) in 1983.
In August 1979, when Mizunuma was a Hosei University student, he was selected Japan U-20 national team for 1979 World Youth Championship.
In April 1984, Mizunuma was selected Japan national team for 1984 Summer Olympics qualification.
He was a soccer commentator for NBS on TV Kanagawa, and also a personality for "Kickoff !!
Furthermore, on 24 August 2006, he was appointed as a coach after Takeshi Okada resigned due to poor results.
Although his team was prevented from being demoted to J2, he continued to be sluggish due to his inauguration without a concrete strategy, and decided to resign after the Emperor's Cup.
In February 2008, it was announced that he would be reappointed as coach of the Hosei University Athletic Association Soccer Club.
On January 22, 2012, he was elected as the director of Yokohama F. Marinos Old Boys at the Naoki Matsuda Memorial Game.