After going to Waseda University, in 1991, Masuho was called up in the Japan national team at 19 years and 3 months, becoming at the time the youngest player of the Japanese national team in the post-war period, debuting against USA at Chicago, on 4 May.
In 1994, he joined Kobe Steel and was active as a central player since his first year in the team.
In the 1995 Rugby World Cup, he was bashed by the media as one of the responsibles for the defeat against New Zealand, but after that, he was feeling about being overweight since his college days, later, he got in shape, regaining his original physique and then returned to the national side.
Between 1999 and 2000, he achieved two consecutive victories in the Japan Company Rugby Football Championship.
After retiring from his player career in 2004, Masuho was appointed coach for Kobelco Steelers.