興国寺, Buddhist temple in Toyama, Japan

Kōkoku-ji is a Rinzai-shū Kokutai-ji-ha temple in the Furuichi district of Toyama, with the mountain name Taiheizan. Its grounds hold the mortuary tablet of the Nanbokuchō-period shugo Momoi Naotsune, inscribed "Kōkoku-ji-den Nintaku Sōgi Daizenjōmon", and east of the main hall a group of medieval stone monuments serves as his memorial stupa. A maple tree once regarded as his grave marker died in 2008.

Kōkoku-ji was founded between 1340 and 1346, during the Southern Court's Kōkoku era, by the Echū shugo Momoi Naotsune, with Shūhō Yūki of the Rinzai Tōfuku-ji Rikkitsu school as founding abbot. A memorial tablet inscribed "Kōkoku-ji-den Nintaku Sōgi Daizenjōmon" is kept for Momoi Naotsune, and east of the main hall stands a group of medieval stone monuments including his memorial tower. Legend holds that Saitō Tatsuoki of Mino became restorer-abbot after years of wandering. The temple was protected by the Fusechi and later Toyama domains, and has belonged to the Kokutai-ji school since the Meiji era.

The temple's name comes from the Nanboku-chō era: it was founded during the Southern Court's Kōkoku years (1340–1346) by Shuhō Yūki for the shugo of Etchū, Momoi Naotsune, whose memorial tablet, inscribed "Kōkoku-ji-den Nintaku Sōgi Daizenjōmon", is kept here. Legend says Saitō Tatsuoki of Mino became its restorer after years of wandering. It belongs to the Rinzai Kokutaiji school and is stop 28 on the Higashi-Etsu Thirty-Three Kannon pilgrimage.

Kōkoku-ji stands in the Nunohiki district of Toyama, a short walk from Nunohiki Station on the Toyama Chihō Railway Kamidaki Line. The temple is the 28th stop on the Higashi-Etsu Thirty-Three Kannon Pilgrimage, so visitors may encounter henro pilgrims. Look east of the main hall for the medieval stone tower group.

East of the main hall stands a group of medieval stone monuments, including a memorial stupa for the temple's founder, the Echū governor Momoi Naotsune. His memorial tablet, inscribed "Kōkoku-ji-den Nintaku Sōgi Daizenjōmon," is kept inside the temple. A venerable maple said to have marked his grave stood on the grounds until it died in 2008.