Sotobō Line

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Sotobō Line
Wakashio 255.E257 in ōami.png
Sotobō Line Wakashio limited express service, November 2017
LocaleChiba Prefecture
TypeHeavy rail
Operator(s)JR East
Line length93.3 km (58.0 mi)
Track gauge1,067 mm (3 ft 6 in)
Operating speed110 km/h (70 mph)
Route map
JR Sotobo Line linemap.svg

The Sotobō Line (外房線, Sotobō-sen) is a railway line in Japan operated by the East Japan Railway Company (JR East) adjacent to the Pacific Ocean, on the eastern (i.e., outer) side of the Bōsō Peninsula. It connects Chiba Station in Chiba to Awa-Kamogawa Station in Kamogawa, passing through Ōamishirasato, Mobara, Chōsei, Ichinomiya, Isumi, Onjuku, and Katsuura. The line is connected to the Uchibō Line at both ends. South of Kazusa-Ichinomiya is single track, and north of Kazusa-Ichinomiya is double track.


In addition to local services, limited express and Rapid ("Commuter Rapid") services run on this line.

Tokyo – (Keiyō Line) – SogaAwa-Kamogawa
(some operate as all-stations "Local" services between Katsuura and Awa-Kamogawa

Station list[edit]

  • ● : All trains stop
  • (●) : Some trains stop
  • | : All trains pass
  • Local trains stop at every station.
Station Japanese Distance (km) to/from

Keiyō Line


Sōbu Line (Rapid) and Yokosuka Line

Transfers Location
(in Chiba)
Keiyō Line Rapid Keiyō Line

Commuter Rapid

Limited express
Sōbu Line Rapid Limited express
Shinjuku Wakashio

(Weekends only)

Chiba 千葉 0.0 JO Sōbu Line (Rapid) (JO28) (some through services)

JB Chūō-Sōbu Line (JB39)

Sōbu Main Line

Narita Line

Chiba Urban Monorail Line 1, Line 2

KS Keisei Chiba Line (Keisei Chiba: KS59)

Chūō-ku, Chiba
Hon-Chiba 本千葉 1.4 |  
Soga 蘇我 3.8 JE Keiyō Line (some through services)

Uchibō Line

Kamatori 鎌取 8.8 | |   Midori-ku, Chiba
Honda 誉田 12.6 | |  
Toke 土気 18.1 (●) |  
Ōami 大網 22.9 Togane Line Ōamishirasato
Nagata 永田 25.3 (●) | | | |  
Honnō 本納 27.7 (●) | | | |   Mobara
Shin-Mobara 新茂原 31.4 (●) | | | |  
Mobara 茂原 34.3  
Yatsumi 八積 38.9 (●) | | | |   Chōsei
Kazusa-Ichinomiya 上総一ノ宮 43.0   Ichinomiya
Torami 東浪見 46.2 | |  
Taitō 太東 49.3 | |   Isumi
Chōjamachi 長者町 52.1 | |  
Mikado 三門 53.7 | |  
Ōhara 大原 57.2 Isumi Line
Namihana 浪花 60.5 | |  
Onjuku 御宿 65.4   Onjuku
Katsuura 勝浦 70.9   Katsuura
Ubara 鵜原 74.5   | |  
Kazusa-Okitsu 上総興津 77.2 (●)  
Namegawa-Island 行川アイランド 80.5 | |  
Awa-Kominato 安房小湊 84.3   Kamogawa
Awa-Amatsu 安房天津 87.7 | |  
Awa-Kamogawa 安房鴨川 93.3 Uchibō Line (some through services)

Rolling stock[edit]

Local service

Keiyō Line through service

Between Soga and Katsuura:

Sōbu Line (Rapid) through service

Between Chiba and Kazusa-Ichinomiya:

Wakashio Limited Express

Former rolling stock[edit]

  • 113 series EMUs (Sotobō Line local services, until 2011)
  • 211-3000 series 5-car EMUs (Sotobō Line local services from 21 October 2006 to spring 2013)[1]


Mobara handcar line
A former handcar converted with a petrol engine at Ohara

The Boso Railway opened the Chiba to Oami section in 1896, extending the line to Kazusa-Ichinomiya the following year and to Ohara in 1899. The company was nationalised in 1907. The extension to Katsuura opened in 1913, to Kazusa-Okitsu in 1927, and Awa-Kamogawa in 1929.

A new tunnel and associated deviation was opened at Toke in 1954 to improve the loading gauge of the line. The Chiba to Soga section was double-tracked between 1960 and 1963, extended to Nagata between 1972 and 1974, with CTC signalling being commissioned between Soga and Awa-Kamogawa in 1974. The line to Kazusa-Ichinomiya was double-tracked between 1980 and 1986, with the Onjuku to Katsuura section double-tracked in 1995, and the Torami to Chojamachi section the following year. The entire line was electrified in 1968, and freight services ceased between 1982 and 1987.

Former connecting lines[edit]

  • Mobara Station: The Mobara Town Council operated a 9 km, 610 mm (2 ft) gauge handcar line to Tai Muko between 1909 and 1924. The council then decided to build a railway to connect to the Kominato Line. 12 km of 1,067 mm (3 ft 6 in) gauge line was opened as far as Okuno between 1930 and 1933, the first 6 km following the handcar line alignment. Poor patronage and economic circumstances led to the line being closed in 1939.
  • Ohara Station: The Chiba Prefectural Government opened a 16 km, 610 mm (2 ft) gauge handcar line to Otaki in 1912. A railcar was converted to petrol engine power in 1922. The line closed in 1927 to allow for the construction of the Isumi Line, which opened on the same alignment in 1930.


On 8 May 2020, at 3:55 pm, the front carriage of a local service derailed between Awa-Kamogawa and Awa-Amatsu stations. Around 20 passengers and crew were on board the train (a 209 Series) when it derailed. One person was taken to a hospital.[2]


  1. ^ "10/21, 房総211系, 営業運転開始" [Boso 211 series enter service]. Japan Railfan Magazine (in Japanese). Vol. 47, no. 549. Japan: Koyusha Co., Ltd. January 2007. p. 179.
  2. ^ "ほぼ直線…外房線先頭車両が脱線 原因は?". (in Japanese). 8 May 2020. Retrieved 9 May 2020.

External links[edit]