This is the Third Amaryu River Bridge, or "Ponkotan Bridge," one of the remnants of the former JR Fukana Line that remains not far from the Roadside Station "Mori to Lake no Sato Horokanai.
It crosses the Uryu River, which runs parallel to National Route 275, and has been preserved by the preservation society even after the Fukana Line was closed down, and was selected as a "Civil Engineering Heritage Site" by the Japan Society of Civil Engineers in 2009.