Rumoi Main Line

The line was laid down as a planned route under the Hokkaido Railway Construction Act, intended to serve Rumoi Port, the leading harbour of the Teshio region on the northern Sea of Japan coast. The first section, built and run by the government railways as the Rumoi Line, opened between Fukagawa and Rumoi (a distance of 31.1 miles, about 50.1 km) on 23 November 1910, bringing into service intermediate stations including Chikushi (later Chippubetsu), Numata, Ebishima, Tōgeshita, Horonuka, Fujiyama and Ōwada. The line was then extended from Rumoi onward to Mashike (10.4 miles, about 16.7 km) on 5 November 1921, reaching its full length and opening the coastal stations leading to the port town.

After 1927 the railway was pushed further north of Rumoi toward Ōtoki and beyond; but on 10 October 1931 those coastal extensions (the Rumoi–Kotanbetsu portion, 44.1 km) were split off and renamed the Haboro Line, and on the same day the Fukagawa–Rumoi–Mashike trunk of 66.8 km was reclassified and renamed a "main line". The route passed to Japanese National Railways (JNR) on 1 June 1949 when the public corporation was established. Through the postwar decades it carried not only local trains but a succession of named semi-express and express services — the Rumoi, Haboro and Mashike among them — some running through onto the Haboro Line; the last of these premium trains, the Rumoi and Haboro, were withdrawn on 1 November 1986.

The line suffered one of its gravest accidents on 14 March 1946, when the rearmost carriage of a down train was derailed by snow damage on the Nobushabetsu River bridge between Reuke and Shaguma and fell into the river, killing 17 people and injuring 67. In its JNR years the line handled heavy rail freight, and many of its stations were fitted with passing loops; as goods traffic was cut these were progressively removed. Freight working on the Rumoi–Mashike section ended on 2 October 1978, and the broader decline of rail freight steadily eroded the line's original purpose.

With the division and privatisation of JNR on 1 April 1987, JR Hokkaido took over the whole line as its primary railway operator, while Japan Freight Railway (JR Freight) held secondary running rights for goods between Fukagawa and Rumoi until relinquishing them on 1 April 1999. On 1 April 1997 the kanji used for the line and its principal stations was modernised — the old form 留萠 giving way to 留萌 — producing the present written name 留萌本線. As private cars and the parallel Fukagawa–Rumoi Expressway drew passengers away — daily traffic on the Rumoi–Mashike section having fallen from about 480 in 1987 to 39 by 2014 — JR Hokkaido began to signal that it could no longer sustain the route on its own.

On 10 August 2015, amid a company-wide retrenchment, JR Hokkaido formally notified the mayors of Rumoi and Mashike that it intended to close the lightly used 16.7-kilometre Rumoi–Mashike section. After the municipalities accepted, the railway filed for abolition and, with the closure date brought forward, the final train ran on 4 December 2016 and the section closed the following day, 5 December 2016, withdrawing eight stations from service. In a November 2016 announcement JR Hokkaido placed the surviving Fukagawa–Rumoi stretch among the lines it could not maintain alone, opening years of negotiations with the four municipalities along the route over its future.

Unable to agree terms for keeping the line open, the parties settled on a two-stage closure: JR Hokkaido proposed in July 2022, and the four municipalities agreed on 30 August 2022, to abolish Ishikari-Numata–Rumoi in spring 2023 and the remainder by spring 2026. The 35.7-kilometre Ishikari-Numata–Rumoi section accordingly closed on 1 April 2023, with the last train on 31 March 2023; the closure removed rail service from the Rumoi Subprefecture and left the surviving 14.4-kilometre Fukagawa–Ishikari-Numata stub as, for a time, the shortest line in Japan still classified as a "main line".

The final act was the abolition of that last 14.4-kilometre section. Through running with the Hakodate Main Line ended at the timetable revision of 14 March 2026, after which the line ran on a temporary schedule, and the Fukagawa–Ishikari-Numata section closed on 1 April 2026 with its last train on 31 March 2026. With this the Rumoi Main Line was abolished in its entirety and its name disappeared from the register of JR line designations — the first complete closure of a JR line since the Sankō Line. The disused right-of-way and station buildings were progressively handed to the local towns or removed, the former Mashike station being preserved as a tourist site.

• 191023 November: the government railways open the line as the Rumoi Line, between Fukagawa and Rumoi (31.1 miles, about 50.1 km).
• 19215 November: the line is extended from Rumoi to Mashike (10.4 miles, about 16.7 km), reaching its full 66.8 km length.
• 193110 October: the coastal Rumoi–Kotanbetsu portion (44.1 km) is split off and renamed the Haboro Line, and the Fukagawa–Rumoi–Mashike trunk (66.8 km) is renamed a 'main line'.
• 194614 March: the rear carriage of a down train is derailed by snow damage on the Nobushabetsu River bridge between Reuke and Shaguma and falls into the river; 17 people are killed and 67 injured.
• 19491 June: the line is transferred to Japanese National Railways (JNR) on the corporation's establishment.
• 19782 October: freight operations on the Rumoi–Mashike section are discontinued.
• 19861 November: the express services Rumoi and Haboro are withdrawn, ending premium-grade trains on the line.
• 19871 April: with the privatisation of JNR, JR Hokkaido takes over the whole line as primary operator; JR Freight becomes secondary operator Fukagawa–Rumoi.
• 19971 April: the kanji used for the line and its main stations is modernised from the old form 留萠 to 留萌, giving the present name Rumoi Main Line (留萌本線).
• 19991 April: JR Freight discontinues its secondary freight operations between Fukagawa and Rumoi.
• 201510 August: JR Hokkaido formally notifies the mayors of Rumoi and Mashike of its plan to close the 16.7 km Rumoi–Mashike section.
• 20165 December: the Rumoi–Mashike section (16.7 km, eight stations) closes; the final train ran on 4 December.
• 202230 August: the four lineside municipalities agree to a two-stage closure — Ishikari-Numata–Rumoi by spring 2023 and the remainder by spring 2026.
• 20231 April: the Ishikari-Numata–Rumoi section (35.7 km) closes (final train 31 March), removing rail from Rumoi Subprefecture; the 14.4 km remnant becomes the shortest 'main line' in Japan.
• 202614 March: through service via the Hakodate Main Line ends at the timetable revision; 1 April: the final Fukagawa–Ishikari-Numata section (14.4 km) closes (last train 31 March), abolishing the whole line and removing its name from the JR line register.