Nagaoka is a city located in Niigata Prefecture, Japan. It is the second largest city in the prefecture, after the capital city of Niigata. As of 4 August 2021, the city had an estimated population of 264,611 in 109,283 households and a population density of 300 inhabitants per square kilometre (780/sq mi). The total area of the city was 891.06 square kilometres (344.04 sq mi).

The Shinetsu Main Line is a railway line, consisting of three geographically separated sections, operated by the East Japan Railway Company in Japan. It was originally one continuous line connecting Takasaki and Niigata via Nagano. Since the opening and later extension of the Hokuriku Shinkansen, sections running in parallel have either been discontinued or transferred to third-sector railway companies.