Yokoyama was born in Saitama on January 21, 1943. After graduating from Rikkyo University, he joined his local club Mitsubishi Motors in 1966. He played as regular goalkeeper from first season and played all matches in Japan Soccer League until 1974. In 1975, he was deprived of regular goalkeeper by Mitsuhisa Taguchi. The club won the league champions 2 times (1969 and 1973) and the 2nd place 6 times. The club also won 1971 and 1973 Emperor's Cup. He retired in 1977. He played 136 games in the league. He was selected Best Eleven 7 times.