Nishitetsu Amagi Line

The line began as part of the network of the Mitsui Electric Tramway (三井電気軌道), a tramway company that built a 1,435 mm gauge line electrified at 600 V DC. The Mitsui Electric Tramway first opened a section between Hiyoshimachi and Fukushima on 18 July 1913. The portion that survives as today's Amagi Line followed two years later: the segment from Kitano to Miyanojin opened on 15 October 1915, and a further stretch from Kushibara to Hiyoshimachi opened on 27 September 1916.

The tramway was extended northeast toward Amagi in the early 1920s. The section from Amagi to Kitano opened on 8 December 1921, bringing the rails to the town of Amagi. On 13 March 1924 a concurrent track was laid across the newly completed Shin-Miyanojin Bridge over the Chikugo River, opening the Miyanojin–Kushibara section and completing a through route between Amagi and Fukushima.

Corporate control of the line changed hands twice over the following two decades. On 30 June 1924 the Kyushu Railway — the predecessor of the Nishitetsu Tenjin Ōmuta Line — absorbed the Mitsui Electric Tramway, and the route became known as the Mitsui Line. On 19 September 1942 the Kyushu Railway was merged into the Kyushu Electric Tramway, which on 22 September 1942 was renamed Nishi-Nippon Railroad; the route became that company's Mitsui Line.

A major reorganisation came in 1948. On 9 November the line's voltage was raised from 600 V to 1,500 V DC, and the former tramcars were replaced by 200-series cars running through to Hanabatake on the Ōmuta Line. On 11 November the Miyanojin–Hiyoshimachi section was suspended, and the Mitsui Line was split: the Amagi–Miyanojin portion was renamed the Amagi Line, while the Hiyoshimachi–Fukushima portion became the Fukushima Line. Ten days later the Miyanojin–Gakkōmae section was relocated to connect with the Ōmuta Line. The suspended Miyanojin–Hiyoshimachi section was formally abolished on 25 April 1952, and the Fukushima Line was closed on 27 November 1958. On 1 August 1960 the Amagi–Miyanojin line was reclassified from the Tramways Act to the Local Railways Act.

From the late 1980s the line was modernised. On 25 April 1989 air-conditioned 600-series cars entered service — the first such cars on the Amagi Line — and the 200-series was withdrawn; from 1 October 1989 wanman (driver-only) operation began on the Amagi–Hanabatake section. On 10 November 2001 a through limited service between Amagi and Ōmuta began, operated as wanman, and 7000-series cars entered service; 7050-series cars followed in March 2003 and the 600-series was retired in September 2004.

In more recent years the line has seen ticketing and operational updates. The nimoca IC card was introduced on 18 May 2008. Station numbering was rolled out across all of Nishitetsu's stations, including those on the Amagi Line, on 1 February 2017, the line carrying the letter "A". A centralised station-management system was introduced on 1 April 2021, making several stations unstaffed, and on 8 December 2021 the line marked the 100th anniversary of the full opening of the Amagi–Kitano section.

• 191318 July: the Mitsui Electric Tramway opens its first section, Hiyoshimachi–Fukushima (later the Fukushima Line).
• 191515 October: the Kitano–Miyanojin section opens — the portion that survives as today's Amagi Line.
• 191627 September: the Kushibara–Hiyoshimachi section opens.
• 19218 December: the Amagi–Kitano section opens, bringing the rails to Amagi.
• 192413 March: a concurrent track over the new Shin-Miyanojin Bridge opens the Miyanojin–Kushibara section, completing the Amagi–Fukushima through route. 30 June: the Kyushu Railway absorbs the Mitsui Electric Tramway; the route becomes the Mitsui Line.
• 194219 September: the Kyushu Railway is merged into the Kyushu Electric Tramway; on 22 September the latter is renamed Nishi-Nippon Railroad, and the route becomes its Mitsui Line.
• 19489 November: voltage raised from 600 V to 1,500 V DC, with 200-series cars running through to Hanabatake. 11 November: Miyanojin–Hiyoshimachi suspended; the Mitsui Line is split into the Amagi Line (Amagi–Miyanojin) and the Fukushima Line (Hiyoshimachi–Fukushima).
• 195225 April: the suspended Miyanojin–Hiyoshimachi section is formally abolished.
• 195827 November: the Fukushima Line is closed.
• 19601 August: the Amagi–Miyanojin line is reclassified from the Tramways Act to the Local Railways Act.
• 198925 April: air-conditioned 600-series cars enter service, the first on the line, and the 200-series is withdrawn. 1 October: wanman (driver-only) operation begins on the Amagi–Hanabatake section.
• 200110 November: a through wanman service between Amagi and Ōmuta begins, and 7000-series cars enter service.
• 2003March: 7050-series cars enter service.
• 200818 May: the nimoca IC card is introduced.
• 20171 February: station numbering is introduced across all Nishitetsu stations, the Amagi Line carrying the letter "A".
• 20211 April: a centralised station-management system is introduced, making several stations unstaffed. 8 December: the line marks the 100th anniversary of the full opening of the Amagi–Kitano section.