The precursor to the line opened in 1915 as the Iwate Light Railway (岩手軽便鉄道), a 762 mm (2 ft 6 in) light railway extending 65.4 km from Hanamaki to Sennintōge Station (仙人峠).
The original plan was to link with Kamaishi Mine and Kamaishi Port, but at an altitude of 887m, the mountain pass at Sennintōge prevented immediate expansion eastward to Kamaishi.
A ropeway conveyor was used to convey goods onward to Ōhashi, from where a 16 km 762mm (2'6") gauge mining railway (which operated between 1915 and 1965) provided the service to Kamaishi.

The railway was nationalized in August 1936, and the line became the "Kamaishi Line".
Motive power for the line was provided by six JNR Class 231 steam locomotives, built by Baldwin Locomotive Works in the USA, and numbered 231 to 236.
Work started on upgrading and re-gauging the line, and the first section, the 31.2 km from Hanamaki to Kashiwagidaira was regauged to the standard Japanese track gauge of 1,067 mm (3 ft 6 in) and re-opened from September 1943.
The mining railway between Rikuchū-Ōhashi and Kamaishi was also upgraded to 1,067 mm gauge by October 1944 to meet the urgent need for increased capacity to transport iron ore during the war period, and was named the Kamaishi East Line (釜石東線, Kamaishi-Higashi-sen).
The entire 90.2 km line was finally completed between Hanamaki and Kamaishi in June 1950, opening to traffic on 10 October of that year.
The precursor to the line opened in 1915 as the Iwate Light Railway (岩手軽便鉄道), a 762 mm (2 ft 6 in) light railway extending 65.4 km from Hanamaki to Sennintōge Station (仙人峠). The original plan was to link with Kamaishi Mine and Kamaishi Port, but at an altitude of 887m, the mountain pass at Sennintōge prevented immediate expansion eastward to Kamaishi. A ropeway conveyor was used to convey goods onward to Ōhashi, from where a 16 km 762mm (2'6") gauge mining railway (which operated between 1915 and 1965) provided the service to Kamaishi.
The railway was nationalized in August 1936, and the line became the "Kamaishi Line". Motive power for the line was provided by six JNR Class 231 steam locomotives, built by Baldwin Locomotive Works in the USA, and numbered 231 to 236. Work started on upgrading and re-gauging the line, and the first section, the 31.2 km from Hanamaki to Kashiwagidaira was regauged to the standard Japanese track gauge of 1,067 mm (3 ft 6 in) and re-opened from September 1943. The mining railway between Rikuchū-Ōhashi and Kamaishi was also upgraded to 1,067 mm gauge by October 1944 to meet the urgent need for increased capacity to transport iron ore during the war period, and was named the Kamaishi East Line (釜石東線, Kamaishi-Higashi-sen). The entire 90.2 km line was finally completed between Hanamaki and Kamaishi in June 1950, opening to traffic on 10 October of that year.
Kamaishi Line