In October 1964, when Yokoyama was a Rikkyo University student, he was selected the 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. After that, Yokoyama became a regular goalkeeper at Japan national team. In 1968, he was selected Japan for 1968 Summer Olympics in Mexico City. He played all matches and Japan won Bronze Medal. In 2018, this team was selected Japan Football Hall of Fame. He also played at 1966, 1970 and 1974 Asian Games. He played 49 games for Japan until 1974.