was a town located in Tagata District, Shizuoka Prefecture, Japan in northern Izu Peninsula.
As of March 1, 2005, the town had an estimated population of 15,339 and a density of 928.5 persons per km<sup>2</sup>. The total area was 16.52 km<sup>2</sup>. The town was served by a station on the Izuhakone Railway.
On April 1, 2005, Izunagaoka, along with the towns of Nirayama and à Âhito (all from Tagata District), was merged to create the city of Izunokuni and thus it no longer exists as an independent municipality.
Izu-Nagaoka was established on April 1, 1889 as Kawanishi Village. It was renamed Izunagaoka Town on November 3, 1934.