Chichibu Main Line

The line's oldest section was built not by Chichibu Railway but by its predecessor, the Jōbu Railway (上武鉄道), which opened the stretch between Kumagaya and Yorii on 7 October 1901 using steam haulage. Construction then pushed westward up the Arakawa valley in stages: the Yorii–Hagure section opened on 2 April 1903, and on 14 September 1911 the line was extended from Hagure to a first-generation Chichibu Station near present-day Nagatoro. The company was renamed the Chichibu Railway on 25 February 1916, and on 27 October 1914 the line had already been carried through to the present site of Chichibu Station, with the earlier terminus renamed.

Under the Chichibu Railway name the line continued to grow. The section from Chichibu to Kagemori opened on 27 September 1917, and the separate freight-only Bukō Line from Kagemori toward the limestone workings opened in 1918. Meanwhile a second company, the Hokubu Railway (北武鉄道), built the northern approach across the plain, opening Hanyū to Gyōda on 1 April 1921 and reaching Kumagaya the following year. The Chichibu Railway absorbed the Hokubu Railway on 18 September 1922, joining the two halves of the route into a single line under one operator.

Electrification came in 1922. The Kumagaya–Hodosan (now Nagatoro) section was energised at 1,200 V DC on 20 January 1922, the Chichibu–Kagemori section the next day, and the remaining stretches that May, giving the line electric operation along almost its whole length. The final extension came on 15 March 1930, when the mountain section from Kagemori to Mitsumineguchi opened; it was electrified from the outset. The supply voltage was later raised from 1,200 V to 1,500 V across the whole line on 1 February 1952, the standard the line still uses today.

Freight, above all the carriage of limestone, became the financial backbone of the railway. High-grade limestone quarried from Mount Bukō above Chichibu, and later from Mount Kanō in neighbouring Gunma Prefecture, was hauled down the line in large volumes, and through the 1970s freight accounted for roughly 60 to 70 percent of the Chichibu Railway's rail income, keeping the company in profit. Cement was once carried as well, and the line connected to the national network so that loaded wagons could run through to and from yards beyond Saitama. Although cement shipments have since ceased entirely, limestone traffic continues, and the line's freight tonnage remains among the highest of any private railway in Japan.

The line's fortunes shifted in the 1980s. Falling demand for cement, and the closure in October 1986 of the Tōbu Railway freight yards to which Chichibu trains had run through, pushed much of the traffic onto trucks and tipped the freight business into deficit. Passenger services, by contrast, were developed: a limited-stop "Chichibuji" express began on 1 October 1969, through services with the Seibu Chichibu Line started on 1 April 1989, and one-man operation was introduced on 1 December 1999. On 15 March 1988 the railway launched the "SL Paleo Express," a steam-hauled excursion train using preserved Class C58 locomotive No. 363, which has become one of the line's best-known attractions.

Today the Chichibu Main Line carries a mix of local passenger trains, the "Chichibuji" express, weekend through-running with the Seibu Chichibu Line, the seasonal Paleo Express, and the limestone freight that still defines its operations. Remarkably for a mountain railway, it passes through no tunnels at all over its entire 71.7-kilometre length. PASMO and nationally interoperable IC cards were introduced across all passenger stations on 12 March 2022, and station numbering using the prefix "CR" followed in September that year, leaving the line a modernised but distinctly local railway linking the Kantō Plain with the Chichibu mountains.

• 19017 October: the Jōbu Railway opens the first section, Kumagaya–Yorii, using steam haulage.
• 19032 April: the line is extended from Yorii to Hagure.
• 191114 September: the line is extended from Hagure to a first-generation Chichibu Station near present-day Nagatoro.
• 191427 October: the line is carried through to the present site of Chichibu Station, and the earlier terminus is renamed.
• 191625 February: the Jōbu Railway is renamed the Chichibu Railway.
• 191727 September: the Chichibu–Kagemori section opens.
• 19211 April: the Hokubu Railway opens Hanyū–Gyōda (now Gyōdashi) at the northern end of the route.
• 192220 January: electrification at 1,200 V DC begins (Kumagaya–Hodosan), extended across the rest of the line by May; on 18 September the Chichibu Railway absorbs the Hokubu Railway, uniting the route.
• 193015 March: the mountain section from Kagemori to Mitsumineguchi opens, electrified from the outset, completing the line.
• 19521 February: the supply voltage is raised from 1,200 V to 1,500 V DC across the whole line.
• 19691 October: the limited-stop "Chichibuji" express service begins.
• 1986October: the Tōbu Railway freight yards to which Chichibu trains ran through cease handling freight, accelerating the decline of the line's freight business.
• 198815 March: the "SL Paleo Express" steam excursion train, hauled by preserved Class C58 No. 363, begins running.
• 19891 April: through services with the Seibu Chichibu Line begin.
• 19991 December: one-man (driver-only) operation is introduced.
• 202212 March: PASMO and nationally interoperable IC cards are introduced at all passenger stations; station numbering with the "CR" prefix follows in September.