Itsukaichi Line

The line was built not by the state but by the Itsukaichi Railway, a private company belonging to the Asano zaibatsu. It opened on 21 April 1925 between a temporary Haijima station and Itsukaichi (now Musashi-Itsukaichi), a stretch of about 6.6 miles (roughly 10.62 km) with five stations. Within weeks the company pushed the eastern end the short distance into the permanent Haijima Station, joining the Ōme Electric Railway there on 15 May 1925 and closing the temporary stop. Several original stations were soon renamed — Masuko became Musashi-Masuko in May and Itsukaichi became Musashi-Itsukaichi on 1 June 1925.

Later in 1925 the company extended its line east of the centre as well as into the hills: on 20 September 1925 a branch opened from Musashi-Itsukaichi to Musashi-Iwai, serving the limestone and cement traffic that would dominate the railway for decades. In 1930 the network was completed when, on 13 July, the Itsukaichi Railway opened its own line from Tachikawa to Haijima. This stretch ran on a roundabout southern alignment that paralleled the Ōme Electric Railway (today's Ōme Line), so that two competing railways linked Tachikawa and Haijima. The same year the line's distance posts were converted from miles to kilometres.

On 3 October 1940 the Itsukaichi Railway was absorbed by the Nambu Railway — another Asano-zaibatsu line — and the route became that company's Itsukaichi Line. The Nambu Railway was itself bought out and nationalised in wartime: on 1 April 1944 the line passed to the Ministry of Transport and Communications and became the government's Itsukaichi Line. Because the Tachikawa–Haijima section merely duplicated the parallel Ōme line, it was deemed a non-essential wartime line and suspended on 11 October 1944, never to reopen. A short stretch at its Tachikawa end survives, however, as a connecting line still used by Chūō and Nambu line trains.

With the postwar reorganisation, the line passed to Japanese National Railways (JNR) when that body was established on 1 June 1949. Steam locomotives and old passenger carriages gave way to diesel railcars from 1957, and the whole remaining line from Haijima to Musashi-Iwai was electrified at 1,500 V DC in 1961, after which electric multiple units took over all services. As housing development spread along the valley, the railway's character gradually shifted from a freight carrier to a commuter line, reversing its prewar emphasis.

The decline of the mineral traffic brought the Iwai branch to an end. On 1 February 1971 the Daikuno–Musashi-Iwai section was abolished and passenger services beyond Musashi-Itsukaichi ceased, the remaining stub becoming a freight-only branch as centralised traffic control was installed across the line. That freight branch closed on 15 November 1982, ending all freight operations on the line; bus services now cover the former branch. Following the renaming of Nishi-Akiru to Akigawa on 31 March 1987, the line passed to the newly formed JR East on 1 April 1987 with the privatisation of JNR.

In the JR East era the line has been modernised and steadily integrated into the Tokyo commuter network. New E233 series trains entered service from 18 March 2007, replacing the older stock, and the line was given station numbers (JC) in 2016 as part of a metropolitan-wide scheme. For many years a few rush-hour trains ran through beyond Tachikawa onto the Chūō Line all the way to Tokyo, coupling and dividing at Haijima; from the March 2022 timetable revision these were cut back, leaving only the weekend "Holiday Rapid Akigawa" service, and when that too was withdrawn in March 2023 all through running to the Chūō Line ended. Today the Itsukaichi Line is operated entirely with E233 series units and functions as a short feeder for the western Tokyo suburbs.

• 192521 April: the Itsukaichi Railway, an Asano-zaibatsu company, opens between a temporary Haijima station and Itsukaichi (about 10.62 km) with five stations.
• 192515 May: the line is extended from temporary Haijima to Haijima Station, connecting to the Ōme Electric Railway; the temporary station closes.
• 19251 June: Itsukaichi Station is renamed Musashi-Itsukaichi (Masuko had become Musashi-Masuko on 16 May).
• 192520 September: the branch from Musashi-Itsukaichi to Musashi-Iwai opens, with Daikuno and Musashi-Iwai stations.
• 193013 July: the Itsukaichi Railway opens its own Tachikawa–Haijima line on a southern alignment paralleling the Ōme Electric Railway; that year distance posts switch from miles to kilometres.
• 19403 October: the Itsukaichi Railway is absorbed by the Nambu Railway and the route becomes the Nambu Railway Itsukaichi Line.
• 19441 April: the Nambu Railway is nationalised in wartime; the line passes to the Ministry of Transport and Communications as the government's Itsukaichi Line.
• 194411 October: the Tachikawa–Haijima section, duplicating the parallel Ōme line, is suspended as a non-essential wartime line and is never restored.
• 19491 June: Japanese National Railways (JNR) is established and takes over the line.
• 195719 May: diesel railcars are introduced, replacing steam-hauled trains across the line.
• 196117 February: the whole line from Haijima to Musashi-Iwai is electrified at 1,500 V DC, after which electric multiple units take over all services.
• 19711 February: the Daikuno–Musashi-Iwai section is abolished and passenger service beyond Musashi-Itsukaichi ends; the remaining stub becomes a freight branch and CTC is installed line-wide.
• 198215 November: the Musashi-Itsukaichi–Daikuno freight branch closes, ending all freight operations on the line.
• 19871 April: with the privatisation of JNR (after Nishi-Akiru was renamed Akigawa on 31 March), the line passes to JR East.
• 200718 March: new E233 series trains enter service, replacing the older rolling stock.
• 202212 March: through trains beyond Tachikawa onto the Chūō Line are cut back, leaving only the weekend "Holiday Rapid Akigawa" service.
• 2023March: the "Holiday Rapid Akigawa" service is withdrawn, ending all through running to the Chūō Line.