Seibu Railway Co., Ltd.

The second lineage — from which the present legal entity directly descends — is the Musashino Railway, founded on 7 May 1912, which opened Ikebukuro–Hannō, part of today's Ikebukuro Line, on 15 April 1915 and reached Agano on 10 September 1929. The developer Tsutsumi Yasujirō entered through his company Hakone Tochi (later Kokudo), which from 1924 sold the Ōizumi Gakuen development along the line and in 1928 founded the Tamako Railway. With Musashino in crisis, Tsutsumi began buying up its shares in 1932 and set about rebuilding it; Musashino absorbed the Tamako Railway on 12 March 1940, and that October Tsutsumi secured a majority of the shares and became president. Hakone Tochi gained control of the (old) Seibu Railway in June 1943.

Wartime brought the two railways together in an unusual joint mission: from September 1944, at the request of Tokyo administrator Ōdachi Shigeo, they and the affiliated Shokuryō Zōsan ("Food Production") company hauled night soil out of central Tokyo in trains nicknamed the "golden trains" (last run 1951), after truck disposal collapsed amid gasoline and labour shortages. Against this background the Musashino Railway absorbed the other two companies on 22 September 1945 under the Land Transport Business Coordination Act, becoming the Seibu Agricultural Railway — renamed Seibu Railway on 15 November 1946, with the bus operations spun off into Musashino Jidōsha (now Seibu Bus).

Postwar recovery was distinctive: Seibu built up capacity by rebuilding war-damaged and superannuated national-railway cars at its Tokorozawa works, earning the nickname "the second JNR". On 25 March 1952 the Murayama Line was extended to Seibu-Shinjuku and renamed the Shinjuku Line; in 1963 Seibu became the first private railway in Japan to run 10-car trains, between Ikebukuro and Tokorozawa; and on 14 October 1969 the Seibu Chichibu Line opened together with the 5000 series "Red Arrow" limited express — the 101 series, first of its signature yellow trains, debuted on 5 March that year. After Tsutsumi Yasujirō's death in 1964 his third son Yoshiaki led the group, with Kokudo building Prince Hotels, ski resorts, golf courses and other resort businesses and acquiring in 1978 the Crown Lighter Lions, which became the Seibu Lions. The group became known as the "Seibu kingdom", and Forbes ranked Yoshiaki the world's richest man from 1987 to 1990. The stock was listed on the First Section of the Tokyo Stock Exchange (TSE), but control stayed with the family through Kokudo. On 5 August 1986 the head office moved from Minami-Ikebukuro to Tokorozawa, Saitama.

The family era ended in scandal. In 2004 a sōkaiya payoff affair forced Tsutsumi Yoshiaki to resign the Seibu Railway chairmanship in April; on 13 October came the disclosure that securities reports had been falsified — Kokudo's holding under-reported by 22% and parked under 1,000-plus borrowed names, the top ten holders alone exceeding the TSE's 80% delisting threshold. The shares were delisted on 17 December 2004, and Yoshiaki was arrested on 3 March 2005 on charges under the Securities and Exchange Act. A sweeping reorganisation followed under Gotō Takashi, a Mizuho Corporate Bank executive brought in as president: Kokudo, recapitalised by investors including the American fund Cerberus Capital Management, merged into Prince Hotels on 1 February 2006; on 2 February a share exchange made Seibu Railway a wholly owned subsidiary of Prince Hotels; and the 3 February stock transfer created Seibu Holdings, with Cerberus the largest shareholder at 29.9%. The reorganisation left Seibu Railway a railway-focused operating company. In 2012 and 2013 Cerberus proposed abolishing five unprofitable lines — the Tamagawa, Yamaguchi, Kokubunji, Tamako and Seibu Chichibu lines — and mounted a hostile tender offer that lifted its stake to 35% by June 2013; the proposals were voted down, and Seibu Holdings relisted on the TSE First Section on 23 April 2014.

Today Seibu operates 12 lines totalling 176.6 operating kilometres, divided into the operationally separate Ikebukuro Line and Shinjuku Line systems, which cross at Tokorozawa. Through running onto the Chichibu Railway began on 1 April 1989. Via the Seibu Yūrakuchō Line, trains run through to the Tokyo Metro Yūrakuchō Line (from 26 March 1998) and Fukutoshin Line (from 14 June 2008), and since 16 March 2013 onward to the Tōkyū Tōyoko and Minatomirai lines. The reserved-seat S-TRAIN began on 25 March 2017, the day the 40000 series entered service. The 001 series "Laview", the first new limited express type in 26 years, entered service on 16 March 2019 and won the Blue Ribbon Award in 2020. On 26 September 2023 Seibu announced that it would acquire energy-efficient secondhand cars from Tōkyū and Odakyu as "sustainable rolling stock"; the ex-Odakyu 8000 series entered service on 31 May 2025. Wholly owned by Seibu Holdings and itself the parent of the Saitama Seibu Lions, Seibu Railway is headquartered in Tokorozawa; its registered head office is at Daiya Gate Ikebukuro in Toshima, Tokyo.

• 189421 December: the Kawagoe Railway opened the line from Kokubunji to a temporary station at Kumegawa (today's Higashi-Murayama) — now the Seibu Kokubunji Line — and extended it to Kawagoe (today's Hon-Kawagoe) on 21 March 1895.
• 19127 May: the Musashino Railway, the direct legal predecessor of today's Seibu Railway, was founded; the company marked its 100th anniversary on 7 May 2012.
• 191515 April: the Musashino Railway opened its line from Ikebukuro to Hannō, now part of the Seibu Ikebukuro Line.
• 192716 April: the (old) Seibu Railway opened the Murayama Line from Takadanobaba to Higashi-Murayama, double-tracked and electrified, and began through service between Takadanobaba and Kawagoe — part of today's Shinjuku Line.
• 194522 September: under the Land Transport Business Coordination Act, the Musashino Railway absorbed the (old) Seibu Railway and the Shokuryō Zōsan company and was renamed the Seibu Agricultural Railway; the merger grew out of the night-soil transport operation the three companies had begun jointly for Tokyo during the war.
• 194615 November: the Seibu Agricultural Railway was renamed Seibu Railway, the present company name, and its bus operations were spun off into Musashino Jidōsha (now Seibu Bus).
• 195225 March: the Murayama Line was extended from Takadanobaba to Seibu-Shinjuku and the line was renamed the Shinjuku Line.
• 196914 October: the Seibu Chichibu Line opened, and the 5000 series "Red Arrow" limited express entered service; the first of the company's signature yellow trains, the 101 series, had debuted on 5 March the same year.
• 19865 August: the head office moved from Minami-Ikebukuro, Toshima, Tokyo to Tokorozawa, Saitama Prefecture, where the Ikebukuro and Shinjuku lines intersect.
• 199826 March: mutual through services began with the Teito Rapid Transit Authority (now Tokyo Metro) Yūrakuchō Line via the Seibu Yūrakuchō Line.
• 200417 December: Seibu Railway shares, listed on the First Section of the Tokyo Stock Exchange, were delisted after the 13 October disclosure that securities reports had been falsified — Kokudo's shareholding under-reported by 22%, with shares held under more than 1,000 borrowed names; the exchange had decided on delisting on 16 November.
• 20063 February: the holding company Seibu Holdings was created by stock transfer, two days after Kokudo was merged into Prince Hotels and one day after Seibu Railway became a wholly owned subsidiary of Prince Hotels by share exchange; the reorganisation left Seibu Railway a railway-focused operating company, with Cerberus Capital Management the largest shareholder in Seibu Holdings at 29.9%.
• 201316 March: mutual through services began via the Tokyo Metro Fukutoshin Line (joined on 14 June 2008) onto the Tōkyū Tōyoko Line and the Minatomirai Line; the same year Cerberus's hostile tender offer raised its stake in Seibu Holdings to 35%, but its restructuring proposals — including abolishing five unprofitable lines — were voted down, and Seibu Holdings relisted on the TSE First Section on 23 April 2014.
• 201916 March: the 001 series "Laview", the company's first new limited express type in 26 years, entered service; it won the Blue Ribbon Award on 5 June 2020.