Ōigawa Main Line

The railway company predates the line itself. A licence for a railway in the area was granted to the Sunpu Railway in 1921, and on 1 May 1922 the undertaking changed its name to the Ōigawa Railway. After a 1923 revision of the project to run from Kanaya, the first section of the Ōigawa Main Line opened on 10 June 1927 between Kanaya and Yokooka (a station since closed), worked at first by steam power on 1,067 mm track.

From Kanaya the single-track line was then pushed up the Ōi River valley in stages. A freight-only branch from a junction point to Ibayashi opened in 1928, and in 1929 the line was extended to Ieyama, with passenger service beginning on the earlier freight section. Construction continued through 1930 — reaching Jina by way of a provisional Shiogō station — and on through Shimoizumi and a provisional Aobe station in early 1931. The line reached its present terminus at Senzu on 1 December 1931, completing the through route; the original alignment via Yokooka was abandoned the following day.

The whole Kanaya–Senzu line was electrified at 1,500 V DC on 18 November 1949, with electric locomotive operation beginning that December and electric railcars entering passenger service on 8 August 1951. Express services on the line began in 1971. Running through an isolated mountain district with no large towns and very low population density, the line came to depend chiefly on tourists bound for the hot-spring resorts along the Ōi River and on climbers and hikers heading for the peaks of the Southern Alps.

To boost ridership and the line's popularity, the Ōigawa Railway revived steam operation on the main line on 9 July 1976, becoming Japan's best-known regular steam operator. A varied collection of historic locomotives and carriages is used on both the steam and electric services — including former Kintetsu, Nankai, Keihan and other big-private-railway electric cars kept in their pre-transfer colours — which has made the line a favourite with railway enthusiasts and photographers. Freight services ended in 1983.

In later decades the line added new local stations and leaned further into tourism and heritage. Stations such as Daikanchō (1965), Ōwada (1969), Higiri (1985) and others were opened along the lower part of the route, and on 12 July 2014 the railway launched its "Thomas the Tank Engine" event trains, which became a signature attraction. In November 2018 the Shin-Kanaya station building was registered as a Tangible Cultural Property.

On 24 September 2022, landslides caused by Typhoon Talas (Typhoon No. 15) forced the suspension of the entire line. Service was restored in stages from the Kanaya end — Kanaya to Ieyama reopened on 16 December 2022, and Ieyama to Kawaneonsen-Sasamado on 1 October 2023 — but the section from Kawaneonsen-Sasamado up to Senzu remained out of service as of 2026. With public funding agreed in 2025 toward an estimated cost of about 2.1 billion yen, the Ōigawa Railway is aiming to reopen the whole line around 2029.

• 19216 July: a railway licence is granted to the Sunpu Railway for a line in the Shimada area.
• 19221 May: the undertaking is renamed the Ōigawa Railway.
• 192710 June: the first section, Kanaya–Yokooka (since closed), opens on 1,067 mm track worked by steam power.
• 1929The line is extended to Ieyama, with passenger service starting on the earlier freight-only section.
• 19311 December: the (provisional) Aobe–Senzu section opens, completing the line through to its present terminus at Senzu.
• 194918 November: the whole Kanaya–Senzu line is electrified at 1,500 V DC; electric locomotive operation begins that December.
• 19518 August: electric railcars enter passenger service.
• 19711 January: limited-stop express ('electric express') services begin on the line.
• 19769 July: the Ōigawa Railway revives steam-locomotive operation on the main line, becoming Japan's best-known regular steam operator.
• 19831 October: freight services on the line cease.
• 201412 July: the "Thomas the Tank Engine" event trains begin operating.
• 20182 November: the Shin-Kanaya station building is registered as a Tangible Cultural Property.
• 202224 September: landslides from Typhoon Talas (Typhoon No. 15) suspend the entire line; Kanaya–Ieyama reopens on 16 December.
• 20231 October: service resumes on the Ieyama–Kawaneonsen-Sasamado section; Kawaneonsen-Sasamado to Senzu remains closed.
• 202528 March: public funding is agreed toward the roughly 2.1-billion-yen cost of restoring the closed section, with full reopening targeted around 2029.