Mini-Shinkansen (Japanese:ミニ新幹線) is the name given to the concept ofconverting existing1,067 mm (3 ft 6 in)narrow gauge railway lines to1,435 mm (4 ft 8+1⁄2 in)standard gauge to allow operation ofShinkansen services in Japan. While thetrack gauge is widened, the originalloading gauge is retained, requiring the use of specially designed Shinkansen rolling stock with a narrower cross-section, leading to the "mini-Shinkansen" designation.

Unlike purpose-builthigh-speed Shinkansen lines, mini-Shinkansen routes are constrained by their legacy infrastructure to maximum operating speed of 130 kilometres per hour (81 mph). Two mini-Shinkansen routes have been constructed: theYamagata Shinkansen, which opened in 1992, and theAkita Shinkansen, which opened in 1997. Both connect to the high-speedTōhoku Shinkansen for direct service to and from Tokyo.^[1]

The mini-Shinkansen concept was first considered byJapanese National Railways (JNR), but was not formally proposed until November 1987, following the formation ofEast Japan Railway Company (JR East). The concept involves regauging existing1,067 mm (3 ft 6 in) narrow gauge lines to the1,435 mm (4 ft 8+1⁄2 in)standard gauge used on the Shinkansen network, to allowthrough-running on a main high-speed Shinkansen line. While the track gauge is widened, theloading gauge remains unchanged, requiring specialized rolling stock with a narrower 2.945-metre (9 ft 8 in) cross-section, compared to the standard 3.35-metre (11 ft) width.^[2]

To compensate for the narrower car bodies, these trains generally have 2×2 seating in ordinary class, compared with the 2×3 configuration of typical Shinkansen trains,^[3] and are fitted with retractablegap fillers that flip up at main line Shinkansen stations to bridge the gap between the train and the platform.

Mini-Shinkansen sets are capable of high-speed operation on Shinkansen tracks—up to 320 kilometres per hour (200 mph) for theE6 series—either on their own or coupled to full-sized Shinkansen sets. On converted narrow-gauge lines, they operate at conventional speeds of around 130 kilometres per hour (81 mph), although track improvements can enable higher speeds where feasible.^[4]

The first mini-Shinkansen route was theYamagata Shinkansen, converted from the a 87.1-kilometre (54.1 mi) section of theŌu Main Line betweenFukushima on theTohoku Shinkansen andYamagata inYamagata Prefecture. Conversion work began in 1988, and Yamagata Shinkansen services commenced on 1 July 1992, operated by a new fleet of400 series trains operatingYamabiko services. Trains ran at up to 240 kilometres per hour (150 mph) on the Tōhoku Shinkansen section and 130 kilometres per hour (81 mph) on the Yamagata Shinkansen section.^[5] Following the success of the initial conversion, a further 61.5 kilometres (38.2 mi) of track was re-gauged to reachShinjō, opening on 4 December 1999. The introduction ofE8 series trains on the line in 2024 increased the maximum operating speed on the Tōhoku Shinkansen section to 300 kilometres per hour (190 mph).

Following the success of the Yamagata Shinkansen, a second mini-Shinkansen route was developed fromMorioka inIwate Prefecture, then the northern terminus of the Tōhoku Shinkansen, toAkita inAkita Prefecture. This involved regauging the 75.6-kilometre (47.0 mi)Tazawako Line from Morioka toŌmagari and 51.7 kilometres (32.1 mi) of the Ōu Main Line from Ōmagari to Akita.^[4] The Akita Shinkansen opened on 22 March 1997 withE3 series trains operatingKomachi services.^[5] The introduction ofE6 series trains on the line in 2013 enabled the maximum operating speed on the Tōhoku Shinkansen section to be increased to 320 kilometres per hour (200 mph) in 2014.

The following rolling stock has been built for use on mini-Shinkansen lines:

• 400 series, Yamagata Shinkansen (in service 1992–2010)
• E3 series, Akita Shinkansen (in service 1997–2014) and Yamagata Shinkansen (since 1999)
• E926East i, track and overhead wire inspection train (since 2001)
• E955Fastech 360Z, experimental test train (2006–2008)
• E6 series, Akita Shinkansen (since 2013)
• E8 series, Yamagata Shinkansen (since 2024)

• Gauge Change Train, an experimental train designed to operate on both narrow-gauge and Shinkansen routes
• Super Tokkyū, a concept for building narrow-gauge lines to Shinkansen standards

• Shinkansen
• Railway services introduced in 1992

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