The is an underground electric bus line in Tateyama, Toyama, operated by the Tateyama Kurobe Kankà  Company. Until 2024, it was a trolleybus known as the , officially the , and it was the last trolleybus service in Japan in its final years. Now operated by battery-electric buses, the line is entirely underground (in tunnel), including both termini. The line is a part of the Tateyama Kurobe Alpine Route, a sightseeing route to the Kurobe Dam that also includes bus, funicular and aerial tramway lines.
It was the last remaining trolleybus line in Japan, following the similar conversion of the Kanden Tunnel Trolleybus line to battery operation in November 2018. It was also the last non-museum trolleybus line in the world using right-hand drive vehicles running left-hand. Trolleybus operation was permanently discontinued at the end of the 2024 season. Battery-electric buses took over the service at the beginning of the 2025 season.
The line originally opened as a normal (diesel) bus line in April 1971, but was later re-equipped for trolleybuses. The trolleybus line opened on 23 April 1996.
The Tateyama Tunnel Trolleybus forms a component of the Tateyama Kurobe Alpine Route, a mountain sightseeing route between Tateyama, Toyama and à Âmachi, Nagano. The trolleybus line connects to the Tateyama Highland Bus at its western terminus, and to the Tateyama Ropeway at its eastern terminus.
The trolleybus line operates in an exclusive tunnel through Tateyama (Mount Tate), whose peak reaches a height of . Murodà  Station, the western terminus, is at an elevation of , descending to at the eastern terminus of Daikanbà  Station. Murodà  Station is the highest elevation on the Alpine Route, which ascends from near sea level at Toyama Station.
There are no intermediate stations in the tunnel, and all buses run nonstop between the two stations. The journey takes approximately 10 minutes. The majority of the tunnel is a single lane, with a passing lane provided.
When it was operated with trolleybuses, the Tateyama Tunnel Trolleybus was regulated as a railway under the terms of the , which contains provisions for "special railways," which also covers monorails, suspension railways, and cable railways.
On 11 December 2023, Tateyama Kurobe Kankà  announced plans to discontinue its trolleybus service on 1 December 2024 and replace it with battery-electric bus service from April 2025. In keeping with plans reported in June 2024, the last day of trolleybus service was 30 November 2024. The line was the last trolleybus service in Japan.