Route 50 was designated on 18 May 1953 on the current route as National Route 122, and this was redesignated as Route 50 on 1 April 1963 when the route was promoted to a first-class highway.
References
^"一般国道の路線別、都道府県別道路現況" [Road statistics by General National Highway route and prefecture] (PDF) (in Japanese). Ministry of Land, Infrastructure, Transport and Tourism. Retrieved 19 February 2020.