Furusutobaru Castle (フルスト原城, Furusutobaru jō) is a Ryukyuan gusuku in Ishigaki, Okinawa. It is located on Ishigaki Island next to Miyara Bay. It was listed as one of the Historic Sites of Japan in 1978.

Furusutobaru Castle (the Okinawan word for castle is gusuku, though on Ishigaki they are called tsuku). Fusutobaru-tsuku is said to be the residence of Oyake Akahachi, although there is no evidence of this link, and its origins are obscure. Akahachi was from the neighbouring island of Hateruma, and through strength and charisma, he managed to convince the other chieftains and lords of the Yaeyama Islands to follow him, then declared that Yaeyama would not pay mercilessly heavy tribute to the Ryukyu Kingdom. When this news came to Naha, the court commanded the ruler of Miyako Island, Nakasone Toyomiya to invade and suppress of Yaeyama. Miyako's forces landed in Miyara Bay in 1500. Akahachi was killed, and Nakasone would go on to conquer the rest of Yaeyama and then submitted them to King [[Shō Shin]. The extent to which this story connects with this castle remains moot.

The site sits on a ridge overlooking Miyara Bay. There are 15 walled enclosures, a few of which have been excavated. Finds include local pottery, white porcelain and celadon from China, and the bones of horses and cows.