The is a railway line in Japan, operated by the East Japan Railway Company (JR East). It connects Fukushima Station through Akita Station to Aomori Station. Since the opening of the Yamagata Shinkansen on July 1, 1992, the Fukushima–Yamagata section (as well as the Yamagata–Shinjà  section since 1999) is sometimes referred to as the . The name of the line as a whole refers to the ancient provinces of Mutsu () and Dewa (), as it connects both ends of Mutsu by passing northâÂÂsouth through Dewa.
The à Âu Main Line is split into the following four sections. Due to the differences in the tracks of these sections, there are no trains that go through more than one (with the exception of an AkitaâÂÂShinjà  connection). Local and rapid services on the line are generally operated by 701 series (entire line) and 719 series (FukushimaâÂÂShinjà  only) electric multiple unit trains.
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On this section, which extends for , the à Âu Main Line shares tracks with the Yamagata Shinkansen, a so-called mini-Shinkansen line. Mini-Shinkansen projects convert existing narrow-gauge main lines to standard gauge so that Shinkansen-specification trains can operate directly onto conventional routes.
The tracks were re-gauged between 1988 and 1992, with services commencing on 1 July 1992 under the Tsubasa service name. The rail gauge is to allow Yamagata Shinkansen trains to operate. The à Âu Main Line is known as the Yamagata Line on this section.
====== This section is long, crossing the border between Yamagata and Akita. Demand is relatively low, and all trains except one limited-stop "Rapid" service operate as all-stations "Local" trains.
====== Covering , this section is shared with the Akita Shinkansen, which is also a mini-Shinkansen line converted from narrow gauge to standard gauge. Services began on 22 March 1997 under the Komachi service name. The conversion involved the installation of a parallel single standard-gauge track. On a section between Jingà «ji and Mineyoshikawa, a third running rail was added to the narrow-gauge, allowing mini-Shinkansen trains to operate over either track. The arrangement allows narrow-gauge à Âu Main Line services to continue to operate between Shinjà  and Akita.
====== The northernmost section runs for between Akita and Aomori. Together with the San'in Main Line, Maizuru Line, Obama Line, Hokuriku Main Line (including the IR Ishikawa Railway, Ainokaze Toyama Railway, and the Nihonkai Hisui Line), part of the Shinetsu Main Line (including the Myoko Haneuma Line), Hakushin Line, and the Uetsu Main Line, it forms part of the (Sea of Japan Trans-Japan Line), used by both express and freight services.
Legend:
The Japanese national government built the à Âu Main Line, starting construction from Aomori in 1894, from Fukushima in 1899 and linking the two sections in 1905. In 1909 the formal name of the line was declared.
Opening dates for the individual sections are as follows.
Various sections of the line have been double-tracked since 1963.
The section between Niwasaka and Akaiwa stations proved to be geologically unstable, with one of the original tunnels collapsing in 1910. A realignment involving two new tunnels was opened a year later. Geological instability was suspected as the cause of a derailment on the section in 1948 that killed three crewmen, and another realignment was undertaken when the section was double-tracked in 1968.
Itaya station was originally a reversing station, and was realigned as a through station in conjunction with the gauge conversion work (see below) in 1990.
The Fukushima to Yonezawa section was electrified at 1,500 V DC in 1949, and the Uzen-ChitoseâÂÂYamagata section in conjunction with the Senzan Line (also at 1,500 V DC) in 1960. Trials on the Senzan Line subsequently resulted in the adoption of 20 kV AC for all further electrification, and the abovementioned sections were converted to the new standard when the Yonezawa to Yamagata section was electrified in 1968. The Aomori to Akita section was electrified (at 20 kV AC) in 1971, as was the Akita to Uzen-Chitose section in 1975.
The company also opened a 5 km gauge line to the Hanaoka mine in 1914 including a bridge over the à Âu Main Line at Odate, which was converted to 1,067 mm gauge in 1951 to enable ore wagons to be forwarded via JNR trains. Freight services ceased in 1983 and the line closed in 1985.
Full standard Shinkansen lines are constructed using 1,435 mm gauge track on a separate alignment, with a high speed () and a commensurately high construction cost. Following privatisation and regionalisation of the JNR network in 1987, the JR East company decided to convert the FukushimaâÂÂYamagata section of the 1,067 mm gauge à Âu Main line to 1,435 mm gauge, enabling Shinkansen trains from Yamagata to travel on the Tohoku Shinkansen line through to Tokyo. Called Mini-shinkansen, this was a cost-effective way of providing an improved level of service on the line, although only purpose-built Shinkansen trains can travel on such lines, as the loading gauge was not changed, nor the voltage (full standard Shinkansen lines use 25 kV AC). The Yamagata Shinkansen opened in 1992, and although the maximum speed is , the overall transit time to places beyond Fukushima is improved due to the elimination of the need to change trains at the junction.
The success of this project led to the conversion of the Omagari to Akita section in conjunction with the opening of the Akita Shinkansen in 1997, and the extension of the Yamagata Shinkansen to Shinjo in 1999. These projects also created parallel 1,435 and 1,067 mm gauge lines between Omagari and Akita and between Yamagata and Uzen-Chitose respectively, and a dual-gauge section between Jinguji and Minejoshikawa (on the Omagari to Akita section), enabling Shinkansen trains to pass at speed on the mostly single-track line.
Additionally, local services continue to be provided on the gauge-converted lines by 701-5000 series standard-gauge suburban/interurban rolling stock.
JR East announced on 26 November 2025 that the 701 series and 719 series would be replaced by E723 series trainsets by late 2026.