Keisei Matsudo Line

Most of the line follows the trackbed of a railway laid by the Imperial Japanese Army's Railway Regiment as a practice line (the Railway Regiment training line, Matsudo line) for drilling soldiers in track-laying. To give recruits varied conditions to work under, and to pack a required length of around 45 km of practice track into a limited area, the army built the line with deliberately tight curves and a deliberately tortuous course. That is why, even after the passenger line was straightened as far as possible at its opening, the alignment remains far from ideal to this day. When Japan surrendered at the end of the war the Railway Regiment was disbanded; its rails were sold off to Seibu Railway, but the roadbed itself was left in place, and both Seibu and Keisei quickly took an interest in reusing it.

Both companies hired former regiment officers and lobbied the General Headquarters of the Allied occupation (GHQ) for permission to lay a railway on the route. Keisei, whose business base lay within Chiba, won the contest, and in March 1946 it was authorised to use the roadbed (formal transfer of ownership did not follow until 1955). In October 1946 Keisei set up a subsidiary, Shin-Keisei Electric Railway, to build and run the line. Construction began in January 1947; because new materials were almost impossible to obtain, the builders ranged outside the prefecture to gather up second-hand, non-standard materials. Shortly before opening, GHQ grew uneasy about reviving a former military line and the project was briefly in doubt, but after Shin-Keisei executives made their case the line opened on schedule on 27 December 1947 as the Shin-Keisei Line, running the 2.5 km from the first-generation Shin-Tsudanuma Station to Yakuendai, at 1,067 mm gauge.

The army practice track had been built to an extremely narrow 600 mm gauge; on transfer to Keisei it was regauged to 1,067 mm. The line could not be built to the 1,372 mm gauge of its parent Keisei because the Local Railway Act of the time did not permit that gauge, requiring 1,067 mm (with 1,435 mm or 762 mm allowed only in special cases). The railway then extended outward from the Shin-Tsudanuma end, opening Yakuendai–Takinofudō in 1948 and reaching Kamagaya-Daibutsu and then Kamagaya-Hatsutomi (today's Hatsutomi) by October 1949. Short of construction funds, the company at one point gave up on completing the line through to Matsudo on the Jōban Line and ran buses between Hatsutomi and Matsudo instead; with backing from Mitsubishi Electric — which had taken the Nippon Kentetsu works in lineside Funabashi into its group — construction resumed and the line was carried through to Matsudo.

The Matsudo–Kamihongō section, unlike the rest of the route, was not a former military line but entirely new construction, requiring a plateau to be cut through. On 21 April 1955 the Hatsutomi–Matsudo section opened and the whole Shin-Keisei Line was complete as a single-track railway, and through running onto the Keisei Chiba Line began (it was discontinued that September). The gauge was then changed twice more to align with the parent company's system: to 1,372 mm on 20 October 1953 and to 1,435 mm on 18 August 1959 — both changes coming earlier than Keisei's own regauging, and the line is thought to have doubled as a rehearsal for the parent's conversion.

From the 1960s the line was progressively double-tracked as ridership surged; because much of the army roadbed had been wide enough for two tracks the work went relatively smoothly, and by February 1975 the whole line except the Shin-Tsudanuma–Keisei-Tsudanuma section had been doubled. The maximum speed, raised to 75 km/h in 1988 after 33 years unchanged, was lifted again to 85 km/h in 1996. Through services were run, and later resumed, onto neighbouring lines: reciprocal through running with the Hokusō / Kōdan line operated from 1979 before being discontinued in 1992, and one-way through running onto the Keisei Chiba Line resumed in December 2006. Earlier plans to extend the line beyond Matsudo toward Shibamata and Kōnodai in Tokyo were acquired as licences and even saw land bought up, but local opposition and competing projects caused them to collapse, and the licences lapsed around 1971.

The line's modern transformation came through corporate consolidation. On 31 October 2023 the parent, Keisei Electric Railway, announced that it would absorb Shin-Keisei Electric Railway — which owned the line — by way of a simplified merger effective 1 April 2025, pledging to maintain the route, its stations, its employees' jobs and its fare structure. On 1 April 2025 the merger took effect: Shin-Keisei Electric Railway was absorbed into Keisei Electric Railway, the line was renamed the Keisei Matsudo Line, and the station numbering was reassigned from the Shin-Tsudanuma end as KS-66 to KS-88. No change was made to fares or to the timetable. Because Keisei names its lines after the terminal station or place, no public name contest was held; the route had also reversed its designated direction, with Keisei-Tsudanuma now the starting point and Matsudo the terminus.

• 1946March: Keisei Electric Railway is authorised by GHQ to use the former Army Railway Regiment roadbed (formal transfer of ownership followed in 1955). October: Keisei establishes the subsidiary Shin-Keisei Electric Railway to build and run the line.
• 194727 December: the line opens as the Shin-Keisei Line, running the 2.5 km from the first-generation Shin-Tsudanuma Station to Yakuendai at 1,067 mm gauge; construction had begun that January using second-hand non-standard materials.
• 194826 August: Yakuendai–Takinofudō (4.1 km) opens.
• 19498 January: Takinofudō–Kamagaya-Daibutsu (3.1 km) opens. 7 October: Kamagaya-Daibutsu–Kamagaya-Hatsutomi (today's Hatsutomi) (2.1 km) opens, completing Yakuendai–Kamagaya-Hatsutomi.
• 195320 October: the line is regauged from 1,067 mm to 1,372 mm and begins running into Keisei-Tsudanuma. 1 November: Keisei-Tsudanuma–new Shin-Tsudanuma–Maebara (2.3 km) opens.
• 195521 April: Hatsutomi–Matsudo (13.3 km) opens, completing the Shin-Keisei Line as a single-track railway; through running onto the Keisei Chiba Line begins (and is discontinued that September). The Matsudo–Kamihongō section was entirely new construction, not a former military line.
• 195918 August: the entire line is regauged again, from 1,372 mm to 1,435 mm, to match the standard gauge used by Keisei Electric Railway — earlier than the parent's own conversion.
• 196814 May: the fourth-generation Shin-Tsudanuma Station moves to its present site and Keisei-Tsudanuma–Shin-Tsudanuma (1.5 km including the relocation) opens, while Keisei-Tsudanuma–Fujisakidai–Maebara (2.3 km) is closed.
• 19757 February: Kamagaya-Daibutsu–Kunugiyama is double-tracked, completing double-tracking of the whole line except the Keisei-Tsudanuma–Shin-Tsudanuma section.
• 19799 March: reciprocal through running with the Hokusō Development Railway line (as then named) begins.
• 19928 July: Shin-Kamagaya Station opens; reciprocal through running with the Hokusō / Kōdan line (as then named) is discontinued.
• 19961 April: the maximum speed is raised from 75 km/h to 85 km/h, cutting the Matsudo–Keisei-Tsudanuma running time and tightening the daytime interval to 10 minutes.
• 200610 December: one-way through running onto the Keisei Chiba Line resumes.
• 20251 April: Keisei Electric Railway absorbs Shin-Keisei Electric Railway by a simplified merger (announced 31 October 2023); the Shin-Keisei Line is renamed the Keisei Matsudo Line and station numbers are reassigned KS-66 to KS-88 from the Shin-Tsudanuma end, with no change to fares or timetable.