Erected in the Kamakura period, this is the family temple of the Chofu Mori family. The Buddha hall, which maintains the beauty of the traditional Zen style of temple architecture, is designated as a national treasure. Although this temple was once called Chofuku-ji Temple, it was renamed Kosan-ji Temple after it became the temple for consoling the soul of the first lord of the Choshu Domain, Mori Hidemoto. The temple has provided a venue for many historical events, including Takasugi Shinsaku's raising an army of just 80 people here, which turned the tide toward the Meiji Restoration. In the precincts is a statue of Takasugi Shinsaku on horseback. The Gokyosenkyo Chamber provides a beautiful view of the garden.