The Sotobō Line (外房線, Sotobō-sen) is a railway line in Japan operated by the East Japan Railway Company (JR East) adjacent to the Pacific Ocean, on the eastern (i.e., outer) side of the Bōsō Peninsula.

It connects Chiba Station in Chiba to Awa-Kamogawa Station in Kamogawa, passing through Ōamishirasato, Mobara, Chōsei, Ichinomiya, Isumi, Onjuku, and Katsuura.

A new tunnel and associated deviation was opened at Toke in 1954 to improve the loading gauge of the line.

On 8 May 2020, at 3:55 pm, the front carriage of a local service derailed between Awa-Kamogawa and Awa-Amatsu stations.

Around 20 passengers and crew were on board the train (a 209 Series) when it derailed.