Château de Hakusan, Mountain fortress in Aki Province, Japan

Hakusan Castle is a mountain castle in the former Aki Province, in present-day Shiromachi, Takaya-chō, Higashihiroshima. It sits on a 314-meter hill, 130 meters above the town of Shiroichi, and its highest enclosure is divided into three tiers surrounded by a belt of secondary enclosures, with smaller enclosures on the northwest and south ridges.

Hiraga Hiroyasu, head of the Hiraga clan, built Shiroyama Castle in 1503 after judging his residence at Misonou Castle poorly defended, and made it his seat. It overlooked the market town of Shiroichi, but it was not a strong fortress, so the clan added subsidiary castles such as Takiyama and Shinkai before building Tōzaki Castle. The castle was kept after Tōzaki was finished; its abandonment date is unknown.

The castle's name comes from Mount Shiroyama, the 314-metre hill overlooking the Shiraichi district of Takaya-chō, Higashihiroshima. Within the grounds stands the Uguisu-zuka, a stone monument erected in 1793 by the haiku poet Taga-an Fūritsu, a senior disciple of Shida Yaba, who was himself a pupil of Matsuo Bashō. Below the hill, the Jōkamachi Shiraichi grew around Kōsei-ji, founded by Hiraga Hiroyasu in 1505, where the graves of the Kihara family remain.

The castle sits on Mount Shiroyama, 314 m high with 130 m of relative height, overlooking the streets of Shiraichi. The summit keep area is split into three terraces ringed by a belt of baileys, with smaller baileys on the northwest and south ridges. The site is an unstaffed mountain ruin; paths follow the ridges, so allow time for the climb.

On the castle grounds stands the Uguisuzuka, a stone monument erected in 1793 by the haiku poet Taga-an Fūritsu, a leading pupil of Shida Yaba, who was himself a disciple of Matsuo Bashō. The castle was abandoned at an unknown date.