Ishigaya Kosaku (Japanese: 石谷広策) (1818-1905/6) was a pupil of the Honinbo house and notable Honinbo Shusaku enthusiast. He published Kogyoku Yoin? (1897), Shusaku Koketsu Kifu? (1904), and erected a large, memorial gravestone to Honinbo Shusaku. He acheived 5 dan in 1876.
In his books, Ishigaya gave glowing accounts of Honinbo Shusaku's character/strength and began using the term Go Sage when referring to him. This would influence later appraisal of Honinbo Shusaku, especially in combination with Segoe Kensaku's 10-volume castle games publication, Oshiro Gofu.
- Kogyoku Yoin 敲玉余韻 (1897) - collection of 100 Shusaku games. Available at the Japanese National Diet Library:
- Shusaku Koketsu Kifu 秀策口訣棋譜 (1904) - collection of 100 openings Ishigaya claims commented by Shusaku in conversation. Can't be confirmed because the games have no player names. Also available at the Japanese National Diet Library: