 The line was extended to the current Muroran in 1897.The Japanese Government nationalised the Hokkaido Colliery Railway in 1906, and the Higashi-Muroran - Muroran section was double-tracked in 1910.The section between Oshamambe and Higashi-Muroran was opened between 1923-28 as the by the Imperial Japanese Government Railways, which later became the Japanese National Railways (JNR).