National Route 173 is a national highway of Japan connecting Ikeda, Osaka and Ayabe, Kyoto in Japan, with a total length of 72.4 km (44.99 mi).

Route 173 originally ran from Osaka to Kobe.

The current Route 173 was designated in 1963 from Ikeda to Mizhuo, replacing a section of Route 9 when it was rerouted.

On 1 April 1975 Route 173 was extended over a section of Route 43 to Ayabe.

This article relating to the roads and highways in Japan is a stub.