Raiden Todoroki Bridge, Spiral bridge in Chichibu, Japan.

The Raiden Todoroki Bridge is a pair of prestressed concrete rigid-frame bridges on National Route 140 in Otaki, Chichibu. The upper Otaki Bridge is 345 m long with a maximum span of 125 m; the lower Todoroki Bridge is 270 m long with a maximum span of 75 m. A curved middle section on a cut slope joins them, so the whole reads as one loop crossing the Nakatsu River twice. The deck runs straight on both bridges, and low-intensity lights are set into the side walls.

Construction began in 1996 and the bridge opened in 1998, built by the Water Resources Development Public Corporation to reroute National Route 140 when the Taki-zawa Dam was built; the new road sits about 120 m above the old one. It is structurally two prestressed concrete rigid-frame bridges, Otaki Ohashi (345 m, main span 125 m) and Todoroki Ohashi (270 m, main span 75 m), joined by a curve cut into the hillside. It won the 1999 JSCE Tanaka Prize and a 1999 Good Design Award.

The name "Raiden" comes from the 1998 story Raiden-bō Monogatari, based on the Chichibu "Deidanbō" legend; "Todoroki" is the name of a hamlet whose residents all moved out for the road realignment. At the Todoroki Bōkyō Plaza viewpoint, an information board explains that vanished settlement. A bridge card with photos and data is handed out at the Michi-no-Eki Ōtaki Onsen roadside station.

The bridge is accessible via National Route 140, which provides good access from the surrounding Chichibu area and neighboring communities. The best views of the spiral structure can be seen from the valley floor, particularly from nearby vantage points that overlook the gorge.

The two spans are not the same: Otaki Bridge is 345 m long with a maximum span of 125 m, while Todoroki Bridge measures 270 m with a 75 m main span. Both are prestressed concrete rigid-frame bridges, and the middle section between them was cut into the hillside.