National Route 42 (国道42号, Kokudō yonjūni-gō), also called Kumano Kaidō or Tropical Route is a national highway connecting Hamamatsu, Shizuoka and Wakayama, Wakayama in Japan.

Part of the route requires crossing Ise Bay on the Ise-wan Ferry.

The route passes though the cities of Tahara, Toba, Ise, Matsusaka, Owase, Kumano, Shingū, Tanabe, and Gobō.

At the terminus Wakayama, there is a junction with national route 24 and 26.

On 1 April 1993, the highway was changed by removing the section of Tsu-Matsusaka and adding the Hamamatsu - Matsusaka.