Nishio Line

The older of the two parents was the Nishio Railway, a 762 mm gauge light railway. Its first segment, from Okazaki-shin to (old) Nishio, was opened on 30 October 1911 by a company called the Saisan Tramway, which renamed itself the Nishio Railway on 25 January 1912. Seeking to connect Okazaki on the Tōkaidō Main Line with the towns of Nishio, Hesaka and Yoshida in southern Mikawa, the railway extended its tracks south of Nishio in stages, opening Nishio–Isshikiguchi in February 1915 and reaching (old) Kira Yoshida in August 1915, and it also ran a short branch toward Yoshida Port that opened in February 1916.

The other parent, the Hekikai Electric Railway, was founded as an affiliate of the Aichi Electric Railway (Aiden), the predecessor of Meitetsu, and like its parent it opened electrified at 1,500 V DC. It opened the Imamura (present-day Shin Anjō) to Yonezu section on 1 July 1926, and pushed on to (old) Nishio in 1928, with through-running to the Aichi Electric Railway's Nishio Line beginning that October.

The two systems were drawn together under the Aichi Electric Railway. On 1 December 1926 Aiden absorbed the Nishio Railway and designated the Okazaki-shin–Nishio–Yoshida Port route as its Nishio Line. To allow through-operation with the Hekikai line, Aiden regauged the former Nishio Railway from 762 mm to 1,067 mm and electrified it — the Nishio–Kira Yoshida section on 1 October 1928 and the Okazaki-shin–Nishio section on 1 April 1929, both at 600 V DC — and the Hekikai Electric Railway abandoned its high-speed ambitions and stepped its own voltage down to 600 V to match.

Meitetsu took shape in the 1930s and 1940s. On 1 August 1935 the Aichi Electric Railway merged with the Nagoya Railway (Meigi Railway) to form Nagoya Railroad (Meitetsu), and the line became the Meitetsu Nishio Line. On 1 March 1944 Meitetsu absorbed the Hekikai Electric Railway; the Imamura–Nishio–Mikawa-Yoshida route was reorganised as the Hekisei Line, before being renamed the Nishio Line again on 16 May 1948.

The line's far older inland section did not survive the war. On 16 December 1943 the original Nishio Railway segment between Okazaki-shin and Nishio was suspended as a wartime non-essential line. Part of it — the 2.5 km between Okazaki-ekimae and Fukuokachō — was revived in December 1951 as the Fukuoka Line, but the Fukuokachō–Nishio section was abandoned on 25 November 1959 and the revived Fukuoka Line itself closed on 17 June 1962, leaving only the present Shin Anjō–Kira Yoshida route. With a timetable revision on 27 March 1960 the line's overhead voltage was raised throughout to 1,500 V DC and through-running with the Gamagōri Line resumed; Mikawa-Yoshida Station was renamed Kira Yoshida on 1 November 1960, and Imamura had already become Shin Anjō in 1970.

In the modern era the Nishio Line settled into a commuter role with frequent through-trains from the Nagoya Main Line. Limited expresses, expresses and locals all run on it, and from the 1990s onward expresses increasingly ran through to and from Nagoya. A major rebuilding around the 2008 timetable revision added the new station of Minami Sakurai between Sakurai and Yonezu and brought elevated track and double-tracking to several sections; the 29 June 2008 revision also ended through-running to the Gamagōri Line. With the revision of 16 March 2019 Minami Sakurai was upgraded to an express stop and the line's semi-express category was abolished, leaving limited expresses, expresses and locals as the services that ply the line today.

• 191130 October: the Saisan Tramway opens the Okazaki-shin to (old) Nishio section as a 762 mm gauge light railway, the origin of the later Nishio Railway portion.
• 191225 January: the Saisan Tramway changes its company name to the Nishio Railway.
• 1915The Nishio Railway extends south of Nishio, opening Nishio–Isshikiguchi (13 Feb) and reaching (old) Kira Yoshida (5 Aug).
• 19261 July: the Hekikai Electric Railway, an Aichi Electric Railway affiliate, opens Imamura (present-day Shin Anjō)–Yonezu, electrified at 1,500 V DC; on 1 December the Aichi Electric Railway absorbs the Nishio Railway and names the Okazaki-shin–Yoshida Port route the Nishio Line.
• 19281 October: the former Nishio Railway's Nishio–Kira Yoshida section is regauged from 762 mm to 1,067 mm and electrified at 600 V DC; the Hekikai line is extended to Nishio and through-running with the Aichi Electric Railway Nishio Line begins.
• 19291 April: the Okazaki-shin–Nishio section is regauged from 762 mm to 1,067 mm and electrified at 600 V DC, completing conversion of the former Nishio Railway.
• 19351 August: the Aichi Electric Railway merges with the Nagoya Railway (Meigi Railway) to form Nagoya Railroad (Meitetsu); the line becomes the Meitetsu Nishio Line.
• 194316 December: the original Okazaki-shin–Nishio section of the former Nishio Railway is suspended as a wartime non-essential line.
• 19441 March: Meitetsu absorbs the Hekikai Electric Railway; the Imamura–Mikawa-Yoshida route is reorganised as the Hekisei Line.
• 194816 May: the Hekisei Line is renamed the Nishio Line.
• 196027 March: the line's overhead voltage is raised throughout to 1,500 V DC and through-running with the Gamagōri Line resumes; Mikawa-Yoshida Station is renamed Kira Yoshida on 1 November.
• 196217 June: the revived Fukuoka Line (the surviving Okazaki-ekimae–Fukuokachō remnant of the old inland section) is abandoned, leaving only the present Shin Anjō–Kira Yoshida route.
• 200829 June: a major revision opens the new Minami Sakurai Station between Sakurai and Yonezu, accompanies recent elevated-track and double-tracking work, and ends through-running to the Gamagōri Line.
• 201916 March: Minami Sakurai is upgraded to an express stop and the line's semi-express category is abolished, leaving limited expresses, expresses and locals.