Main Line

The tramway grew out of a private venture. On 14 November 1921 a tramway licence was granted to the Kumamoto Electric Car company, and the Kumamoto Electric Car Co., Ltd. (熊本電車株式会社) was established two days later, on 16 November 1921. The private company did not, however, build the line itself: on 13 April 1923 it transferred its entire body of rights and obligations, including the licences for its planned routes, to Kumamoto City, and was subsequently dissolved. Operation of the tramway thus passed to the municipality before the first rails carried a passenger.

The network opened on 1 August 1924, when the Main Line between Kumamoto-Ekimae and Jōgyōjimachi, together with the Suizenji Line from Suidōchō to Suizenji, began service. The original operator was the Kumamoto City Tram Department (熊本市電車部). This first day established the Main Line as the backbone of the system, linking the railway station to the heart of the city; the lines that opened afterward were extensions and branches hung off this central axis.

The municipal undertaking was repeatedly reorganised in its early decades. On 11 May 1926 the tram operation was merged with the city waterworks to form the Electricity and Waterworks Bureau, and on 21 June 1928 the waterworks were split off again, leaving the Electricity Bureau. Network growth continued through this period: the Kurokami Line from Jōgyōjimachi to Koikaibashi opened on 26 December 1928, and on 20 June 1929 the Harutake Line and the first section of the Kami-Kumamoto Line, from Karashimachō to Danyamamachi, were brought into service. The Kami-Kumamoto Line was extended from Danyamamachi to Kami-Kumamoto-Ekimae on 24 March 1935.

On 1 June 1944 the operator was renamed the Kumamoto City Transportation Bureau, the name it still carries today. The following year brought both expansion and consolidation: the Kengun Line opened from Suizenji-Kōen to the Mitsubishi factory area on 6 May 1945, and on 1 December 1945 the bureau bought out the separate Kumamoto Electric Tramway company, taking its lines under municipal management. The tram system reached its widest extent in the post-war decades before later contraction left the five lines operated today.

In the modern era the Kumamoto City Tram has become known for its greened track. From 26 April 2010 the bureau converted part of the network to a side-reservation layout and launched a "green carpet" (緑のじゅうたん) supporter scheme, planting the trackbed with lawn; the section around the City Hall stop and Tōrichōsuji was greened at that time. On 1 March 2011 the greening was extended along the Tōrichōsuji–Suidōchō section, at the city-centre end of the Main Line, giving the central trunk the strip of lawn-set rails for which the system is now widely recognised.

• 192114 November: a tramway licence is granted to the Kumamoto Electric Car company; the Kumamoto Electric Car Co., Ltd. is established on 16 November.
• 192313 April: the Kumamoto Electric Car company transfers all of its rights and obligations, including its route licences, to Kumamoto City, and is later dissolved.
• 19241 August: the Main Line (Kumamoto-Ekimae–Jōgyōjimachi) and the Suizenji Line (Suidōchō–Suizenji) open; the original operator is the Kumamoto City Tram Department.
• 192611 May: the tram operation is merged with the city waterworks to form the Electricity and Waterworks Bureau.
• 192821 June: the waterworks is split off, leaving the Electricity Bureau. 26 December: the Kurokami Line (Jōgyōjimachi–Koikaibashi) opens.
• 192920 June: the Harutake Line and the first section of the Kami-Kumamoto Line (Karashimachō–Danyamamachi) open.
• 193524 March: the Kami-Kumamoto Line is extended from Danyamamachi to Kami-Kumamoto-Ekimae.
• 19441 June: the operator is renamed the Kumamoto City Transportation Bureau, the name it still uses.
• 19456 May: the Kengun Line opens (Suizenji-Kōen–Mitsubishi factory area). 1 December: the bureau buys out the separate Kumamoto Electric Tramway company, taking its lines under municipal management.
• 201026 April: part of the network is converted to a side-reservation layout and a 'green carpet' supporter scheme begins; the trackbed around the City Hall stop and Tōrichōsuji is greened.
• 20111 March: the track greening is extended along the Tōrichōsuji–Suidōchō section at the city-centre end of the Main Line.