Initially, the line between Hamaotsu Station and Omi-Imazu Station was operated by the Kojak (Kojaku) railway by local interests; the matter of the Kojak (Kojaku) railway became a problem when planning the Kosei Line, because a track in planning was substantially parallel with this line.
元々浜大津～近江今津間に地元資本による江若鉄道が開業しており、路線計画時にほぼ並行する形のこの江若鉄道の扱いが問題となった。