The is the main line of a Japanese private railway operator Odakyū Electric Railway. It stretches 82.5 km from Shinjuku in central Tokyo through the southwest suburbs to the city of Odawara in Kanagawa Prefecture, the gateway to Hakone. It is a heavy commuter line and is also known for its "Odakyū Romancecar" Limited Express service. From Yoyogi-Uehara some trains continue onto the Chiyoda Line of Tokyo Metro and beyond to the East Japan Railway Company Jōban Line.
The entire stretch of the line was opened on April 1, 1927 by the operator. In 1942 Odakyū was merged to Tōkyū and the line was named Odawara Line. After the World War 2 in 1948 the greater Tōkyū was divided and the line was transferred to the newly founded Odakyū.
To Hakone Tozan Railway line, after dual-gauged (1435 mm for Hakone Tozan and 1067 for Odakyū), through operation began in 1950 for touristic interest to Hakone area. A bypass track was laid in 1955 to Matsuda Station on Gotemba Line of the then Japanese National Railways, and Limited Express service started. To function as a bypass to downtown Tokyo, through service to Chiyoda Line of Tokyo Metro commenced in 1978, via Yoyogi-Uehara.
Currently a track upgrading project is carried between Yoyogi-Uehara and Mukōgaoka-Yūen, quadrupling the tracks by Odakyū and level separating by Tokyo metropolitan government. The section between Yoyogi-Uehara and Setagaya-Daita is being worked. Originally a viaduct was planned but changed to underground tracks, and work on the tunnel between Setagaya-Daita and Higashi-Kitazawa is now ongoing.
|Shinjuku||KS ERL||Shinjuku, Tokyo|
|Minami-Shinjuku||-- ---||Shibuya, Tokyo|
|Noborito||KSTE--||Tama Ward, Kawasaki, Kanagawa|
|Yurigaoka||KS----||Asao Ward, Kawasaki, Kanagawa|
|Tsurukawa||KS ---||Machida, Tokyo|
|Sagami-Ōno||KS ERl||Sagamihara, Kanagawa|
|Ebina||KS ER-||Ebina, Kanagawa|
|Hon-Atsugi||KS ERl||Atsugi, Kanagawa|
|Isehara||KS ER-||Isehara, Kanagawa|
|Tsurumaki-Onsen||KS ER-||Hadano, Kanagawa|
|Shin-Matsuda||XX ERl||Matsuda, Ashigarakami District, Kanagawa|
|Kaisei||e--||Kaisei, Ashigarakami, Kanagawa|