After graduating from Kawaguchi High School and Rikkyo University, he joined his local club Mitsubishi Motors in 1966.

In October 1964, when Yokoyama was a Rikkyo University student, he was selected Japan national team for 1964 Summer Olympics in Tokyo.

At this competition, he debuted and played all matches on behalf of Tsukasa Hosaka fractured his hand just before Olympics.

In 1988, he became a manager for Japan national team as Yoshinobu Ishii successor, where he coached Japan in the country's first competitive tournament, the 1988 AFC Asian Cup.

In 1994, he became a manager for Urawa Reds as Takaji Mori successor.

However, the club finished at the bottom in J1 League and he resigned end of season.