Fukuishi Kannon, Buddhist temple in Sasebo, Japan

Fukuishi Kannon, formally Seigan-ji, is a Shingon-shū Chizan-ha temple in Sasebo whose main hall was donated in 1785 by Matsuura Seizan, lord of Hirado Domain. Behind the hall, on the north side of Mount Fukuishi, a sandstone cave eroded by water opens about 60 cm wide and 4 m high; it is called Rakan Cave for the arhat statues said to have been placed there.

Fukuishi Kannon's official name is Seigan-ji, and tradition dates its founding to the Daidō era (806–810). The present main hall was built in 1785 through a donation from Matsuura Seizan, lord of Hirado Domain. The temple is the 27th stop on the Kyushu Saigoku Thirty-three Kannon pilgrimage.

The temple's popular name comes from the boulder (fukuishi) in its grounds, and its formal name is Seigan-ji. Each year from August 8 to 11 the Sennichi Festival is held, when the hibutsu Eleven-faced Kannon is shown publicly; pilgrims who visit during these days are said to gain the merit of 46,000 days of worship.

The temple stands in Fukuishi-chō, Sasebo; the nearest bus stop is Fukuishi Kannon-mae on the Nishihi and Sasebo bus lines, about one minute on foot. The Sennichi Festival runs from August 8 to 11, when the main image is shown publicly and crowds are largest.

The Rakan Cave is a sandstone hollow about 4 metres high with a mouth of roughly 60 centimetres. Tradition says Kūkai placed 500 arhat statues inside; after losses around World War II, 142 remain. It was once counted among the Hirado Eight Views.