The construction of the Tozai Line, Kyoto Municipal Subway, was divided between Kyoto City, which would undertake the section between Daigo and Misasagi (6.3 km) and the section between Sanjo-keihan and Nijo (3.3km), accounting for a total of 9.4 km, and the Japan Railway Construction Public Corporation with the establishment of Kyoto Kosoku Railway Co., Ltd., a joint public-private venture of Kyoto City, Keihan Electric Railway and certain other enterprises that would undertake the section between Misasagi and Sanjo-keihan (3.3 km), which would be replaced by the Keihan Keishin Line.
京都市営地下鉄東西線の建設主体は、醍醐～御陵間6.3kmと三条京阪～二条間3.3kmの計9.4kmは京都市の施工、京阪京津線の置き換え区間となる御陵～三条京阪間3.3kmは京都市・京阪電気鉄道などが出資する第三セクター京都高速鉄道を設立して日本鉄道建設公団の施工となった。