is an 87.8-kilometer long railway line operated mainly by the Hokkaido Railway Company (JR Hokkaido). The line connects Naka-Oguni Station in Sotogahama, Aomori, through the Seikan Tunnel between Honshu and Hokkaido, to Kikonai Station in Kikonai, Hokkaido. The two stations on the Tsugaru-Kaikyo Line, Tappi-Kaitei Station and Yoshioka-Kaitei Station, are inside the Tunnel.