The Gantoku Line (岩徳線, Gantoku-sen) is a 43.7 km (27.2 mi) railway line operated by West Japan Railway Company (JR West) in Yamaguchi Prefecture, connecting Iwakuni Station in Iwakuni and Kushigahama Station in Shūnan.

The line was originally built as a more direct route between its termini than the original San'yō Main Line (see History section below).

Morigahara Junction (森ヶ原信号場, Morigahara Shingōjō) between Kawanishi and Hashirano Stations is the point where the Nishikigawa Seiryū Line diverges from the Gantoku Line.

Between this junction and Kawanishi Station, the two lines share the same track.

[citation needed] Freight services ceased in 1974, and CTC signalling was commissioned on the entire line in 1982.