National Route 46 was originally designated on 18May 1953 as National Route 105, and this was redesignated as National Route 46 when the route was promoted to a primary national highway. The highway was completed in December 1975, but the road over the Ōu Mountains was deemed to be insufficient. An upgraded section of National Route 46, known as the Sengan Road, was completed in November 1977 to supplement the inadequate road over the mountains.