 The lines were nationalized on 1 August 1927, and merged into one, becoming the Hidaka Line.The track gauge was widened to between Tomakomai and Sarufuto on 26 November 1929, and between Sarafuto and Shizunai on 10 November 1931.The line was extended from Shizunai to on 15 December 1933, to on 24 October 1935, and to Samani on 10 August 1937.