Athletics at the 1964 Summer Olympics – Men's 400 metres
The men's 400 metres was the third-shortest of the men's track races in the Athletics at the 1964 Summer Olympics program in Tokyo. It was held on 17 October, 18 October, and 19 October 1964. 55 athletes from 36 nations entered, with 5 not starting in the first round. The first two rounds were held on 17 October, with the semifinals on 18 October and the final on 19 October. The maximum number of athletes per nation had been set at 3 since the 1930 Olympic Congress. The event was won by Mike Larrabee of the United States, the third consecutive and tenth overall victory for an American in the event. Trinidad and Tobago and Poland each earned their first medal in the 400 metres.